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The Magnetic Universe

Lucie Green takes a closer look at how magnetic fields have shaped the cosmos.

The Sun's magnetic field and the release of plasma directly affect Earth and the rest of the solar system. Solar wind shapes the Earth's magnetosphere and magnetic storms are illustrated here as approaching Earth. The white lines represent the solar wind; the purple line is the bow shock line; and the blue lines surrounding the Earth represent its protective magnetosphere. (Image and caption courtesy of NASA Image Gallery)

You can't see it, but it's there. All the time, and all around you. Protecting you from harmful space radiation and preventing our atmosphere from being stripped away by solar winds — it's the Earth's magnetic field.

For most of us, it hardly ever catches our attention. In observational astronomy, the Earth's magnetic poles are far less important than the geographic poles that we rely on to align our equatorially mounted telescopes. Consider this, though: the Earth's magnetic field probably made life on this planet possible, while more distant, cosmic magnetic fields are the reason that pulsars act like radio lighthouses and vast clouds of electrically conducting gas get sculpted into strange and unusual shapes.

As magnetic fields go, Earth's is the one we're most familiar with and its origin lies in the electric currents that flow in the molten iron that makes up our planet's outer core.

Planetary magnetism

Let's take a step back and look at Earth from the surface of the Moon. From here, we can see the land, oceans and atmosphere. What we can't see, however, is how the Earth's magnetic field envelops it all and extends out into space. For most of the time the Moon is inside the Earth's magnetic field. It only pops out for a few days around the time of new Moon. When it does, the Moon moves into the solar wind — the Sun's outer atmosphere that expands into space at a speed of a million miles an hour.

This wind can't penetrate Earth's magnetic field and instead slams straight into it. Although this interaction is invisible to the human eye, it does produce something spectacular: the aurora. As the solar wind pushes against Earth's magnetic field, it adds energy to it that accelerates charged particles down into our atmosphere. When the particles interact with atmospheric gas, they pass their energy on and cause the gas to glow.

The solar wind is blocked from reaching our atmosphere because it too contains a magnetic field. We've learned that any magnetic field that threads through an electrically charged gas (a plasma) is tied to that gas; they can't be easily separated, or decoupled, as the process is known. So when the gusty flow of magnetized plasma reaches the Earth's magnetic field, it flows around it, causing it to move and ripple like a windsock in a breeze. This property prevents the solar wind from reaching our atmosphere and stripping it away, as happened on Mars. It also provides us with protection from electrically charged cosmic rays.

This life-preserving property that planetary magnetic fields have means that it's important to consider them when it comes to studying exoplanets. So far, we're unable to directly observe an exoplanet's magnetic field. But should a technique for detecting them be developed in the future, the presence of a magnetic field around an exoplanet is likely to influence which ones become targets for further study.

The discovery of the Sun's magnetic field came in 1908 and was made by American astronomer George Ellery Hale. It's impossible to look for and study cosmic magnetic fields without the ability to detect them from a distance using electromagnetic radiation. In 1896, Dutch physicist Pieter Zeeman was carrying out experiments when he found that a strong magnetic field could affect the light given off by a "luminous vapor". The spectral lines emitted by the vapor were broadened or, in extreme cases, split into several components. In a paper published in 1897, Zeeman suggested that his discovery might be used to detect cosmic magnetic fields.

Indeed, it was this technique that was used by Hale to detect the magnetic field of sunspots. The Zeeman effect also polarizes the light in particular ways that can be used to understand the strength and direction of the distant magnetic field, allowing astronomers to probe distant magnetism by studying electromagnetic radiation.

In fact, the Sun allows us to investigate cosmic magnetism up close. Observations of the Sun provide a fantastic level of detail that really shows us how dynamic stellar magnetic fields can be. The Sun has an overall magnetic field that connects the north and south magnetic poles, which are close to the heliographic north and south poles, as they are on Earth.

Small-scale magnetism

But closer inspection of the solar atmosphere reveals arches of magnetic field connecting pairs of sunspots and twisted magnetic field structures known as flux ropes. These ropes are revealed because glowing, electrically charged gas traces them out, similar to the way iron filings sprinkled around a bar magnet align themselves to the field lines. If you watch the Sun over time you'll see that these magnetic structures are always changing and often erupt into the Solar System. The Sun's spatially resolved dynamic activity, powered by magnetism, gives us a glimpse of what other stars are also up to. And it's not just main sequence stars that have important magnetic fields.

Pulsars are a sub-set of neutron stars. Formed from the collapsed cores of high-mass stars that have undergone a supernova explosion, they spin extremely rapidly. As they spin, they flash out pulses of radio waves, as if they were cosmic lighthouses. Some of them flash many times a second. When Jocelyn Bell-Burnell discovered pulsars in 1967 they were viewed as curious objects and jokingly labelled LGM for Little Green Men. But the radio flashes can be understood if you combine a very rapidly spinning star with a strong magnetic field.

As a dying star collapses, its magnetic field is also drawn in with the material of the star itself, intensifying the field strength to a trillion times that of the Earth's. The presence of the field causes charged particles to gyrate around the magnetic field lines and when this happens, radio waves can be created. The radio signal will be concentrated at the north and south magnetic poles of the neutron star. The final ingredient in the making of a pulsar is to have an offset between the star's axis of rotation and the axis connecting the magnetic poles. This means that as the neutron star spins, the radio beam will sweep across space and our radio telescopes can detect it. In fact, neutron stars are record holders when it comes to magnetism: another sub-set of these stars harbor the strongest magnetic fields in the Universe, a thousand times stronger than that of the pulsars. These objects are rather unsurprisingly known as magnetars.

Galactic magnetism

The magnetic field of Earth and the magnetic field of the Sun, thanks to the solar wind, are not the only fields we find ourselves immersed in. Our Galaxy, the Milky Way, has a magnetic field too, albeit with a strength tens of thousands of times less than that of the Earth's. What the galactic field does have in common with the Earth, though, is that rotation is at the heart of its existence.

Magnetic fields in astrophysical objects are created by dynamos, a mechanism in which the rotation of an electrically conductive liquid (such as the molten iron in the core of a planet) is converted into magnetic energy. In this way, how fast an astronomical object spins is an important aspect of magnetic fields and dynamos.

In this context we can understand why Earth has a relatively strong field whereas Mars, once thought to be more Earth-like than it is today, doesn't. Inside Earth, the rotating molten shell means its dynamo is still acting. Mars, on the other hand, had a dynamo, but it ceased acting when the interior of this smaller planet cooled and solidified, leaving only a remnant of its magnetic field locked up in its rocks.

When it comes to timescales, stars and planets can take anything from hours to weeks to complete a single rotation. But these bodies have been around for so long that plenty of time has passed during their lifetimes to sustain and even evolve their magnetic fields. For example, the Sun rotates once every 27 days and has been around for 4.5 billion years. Assuming that the rotation rate has been constant during all of this time, the Sun could have spun over 60 billion times. This isn't the case when it comes to galaxies though. Take the Milky Way: our Galaxy rotates once every few hundred million years, which means there has only been time for it to make a few hundred rotations. So, while a dynamo is important for our Galaxy, there are other additional processes that are making an impact and which still need to be understood.

In 2017, a team led by scientists from the Max Planck Institute for Radio Astronomy in Germany published work showing that galaxy observations can be used to investigate magnetic fields when the Universe was much younger too. Their study of a galaxy that is nearly five billion lightyears away allows us to look back into the early Universe to study the history and evolution of magnetic fields, providing insight into a question that astronomers have long wanted to answer: how long have magnetic fields existed for?

Magnetic fields are magnificent and common across the cosmos. From planets and stars, to galaxies and beyond. Along with gravity, magnetism is responsible for shaping and controlling what we observe. So, next time you look up — no matter what you're looking at — remember the invisible force that is helping shape our Universe.

What are magnetic fields?

Magnetism is a force that is intimately related to electricity. Whenever an electric current flows there will be an associated magnetic field in the surrounding space, or more generally, the movement of any charged particle will produce a magnetic field. Try turning your kettle on and off and see if your smartphone's compass app can detect the magnetic field generated as the current runs through the cable.

These fields have a direction, which is why Earth has a north and a south pole. When two magnetic fields come close to each other, they will try to align, potentially causing the physical objects causing them to move — a compass needle has a magnetic field, and so will always try to line up with Earth's field and point north.

Similarly, the motion of a charged particle will change as it passes through a magnetized area, due to the interaction of the electric and magnetic fields. How the direction changes depends on the charge and mass of the particle, the strength and direction of magnetic field and how fast the particle is travelling.

ABOUT THE WRITER
Lucie is a Professor of Physics and a Royal Society University Research Fellow based at the Mullard Space Science Lab.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Getting to the Heart of Pluto

Two years since the New Horizons flyby, Paul Abel reveals how its data is driving new discoveries about the dwarf planet.

Four images from New Horizons' Long Range Reconnaissance Imager (LORRI) were combined with color data from the Ralph instrument to create this global view of Pluto. (The lower right edge of Pluto in this view currently lacks high-resolution color coverage.) The images, taken when the spacecraft was 280,000 miles (450,000 kilometers) away, show features as small as 1.4 miles (2.2 kilometers), twice the resolution of the single-image view taken on July 13 [2015]. By NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute — Public Domain

On 14 July, it will be two years since New Horizons made its historic closest approach of dwarf planet Pluto. Nine years after its launch in 2006, the spacecraft became the first robotic emissary from Earth to survey this frozen enigma, which has spent much of humanity's existence lost in the frozen darkness of the outer Solar System.

Back in the summer of 2015 we looked at the history of Pluto and made some predictions about what New Horizons might reveal. Now we return to those predictions and look at the exciting discoveries that have been made about this fascinating sentry of the distant Kuiper Belt.

A patchwork surface

In the decades following its discovery Pluto remained little more than a speck of light, even when glimpsed by the world's largest telescopes. In 2002-03, the Hubble Space Telescope produced the first map of its surface, which provided tantalizing hints of a patchwork body. While there was speculation about the existence of cryovolcanism and stunning surface features in the 2015 feature, and some might have thought the author was — as Patrick might have said — letting his imagination run riot, after the flyby it seemed that more imagination was needed.

Dominating the surface of Pluto is the bright, heart-shaped feature known as the Tombaugh Regio, where New Horizons has discovered evidence of some spectacular geological activity. The western lobe is formed by the Sputnik Planitia, a vast, smooth deposit of bright carbon-monoxide ice. It is some 1,050x800km in size, making it the largest glacier in the Solar System. To the south we have the mountains Hillary and Norgay Montes. Norgay Montes is about 3.4km high and largely made of water-ice. There is evidence of ice flows here, and hints of structures that resemble frozen lakes. The views from the top of these mountains are likely to be quite spectacular.

High-resolution images of the Sputnik Planitia show it to be formed of polygon convection cells. It is thought that nitrogen and carbon-monoxide ice is warmed by heat welling up from inside the cells, and that this ice then flows down to lower levels. The small pits located in the ice could be the result of the sublimation of nitrogen-ice. There are no surface craters here, and this has led scientists to conclude that this part of Pluto's surface must be younger than 10 million years old. Clearly, Pluto is still geologically active.

Other areas of interest include ancient dark terrain like the whale-shaped Cthulhu Regio: its dark red coloration is due to the presence of complex hydrocarbons called tholins. The cratering of this part of the surface would suggest it to be a few billion years old, certainly much older than the Sputnik Planitia.

The New Horizons data provides two possible candidates for cryovolcanism: Wright Mons and Piccard Mons. These two features are the tallest objects on the surface of Pluto, reaching a height of 4km. A series of dark irregular patches on the equator form the Brass Knuckles region. The dark patches are separated by bright ice-covered mountains, which themselves contain deep canyons and valleys. It seems that there is no dull place on the surface of Pluto!

A lively atmosphere

It had long been thought that Pluto's atmosphere would be interesting. Due to its rather elliptical orbit, the general consensus was that the atmosphere would freeze to the surface as Pluto moved farther from the Sun. However, scientists now believe that Pluto may have an atmosphere for most, if not all, of its long year. Pluto has a substantial axial tilt of about 120°, so as it orbits the Sun one pole is kept in shadow while the other remains in direct sunlight. New Horizons has revealed that methane and nitrogen are distributed all over the surface. This means that there is probably enough ice to sublimate and keep the atmosphere from completely condensing on the surface.

This does not mean that the atmosphere is static: indeed it is far more dynamic than we thought. Over Pluto's long history, changes in the axial tilt mean there may have been times when the atmosphere was much more dense than it is now. It has been suggested that the atmosphere may even become dense enough to allow the existence of lakes of liquid nitrogen on Pluto.

After New Horizons made its closest approach, its Long Range Reconnaissance Imager began to observe the dwarf planet and it made a surprising discovery: surrounding Pluto was a notable atmospheric haze. Unexpectedly, this haze seemed to be composed of several different layers. It is thought to be due to the interaction of Pluto's atmosphere with sunlight. Although the Sun is weak from this far away, it is still sufficient to break up methane in the upper atmosphere, allowing more complex hydrocarbons to form. These slowly fall to colder, lower altitudes, forming the haze. The Sun's ultraviolet rays convert them into compounds called tholins, the compound responsible for the dark coloration on Pluto's surface. This is a general picture however; the exact details have yet to be determined. No doubt there is a complex interplay between the atmosphere and the surface, creating the dramatic topography we have seen. If anything, New Horizons has revealed the atmosphere of Pluto to be just as fascinating and complex as the planet it enshrouds.

Fellow travelers

Pluto does not wander alone in space: it is accompanied by five satellites, Charon, Nix, Kerberos, Hydra and Styx. Charon is around one-eighth the mass of Pluto, and as a result the pair are tidally locked, which means they always present the same face to each other as they move around the Sun. Unlike our own Moon, Charon does not rise and set over the surface of Pluto, it remains fixed in the black sky.

New Horizons surveyed Charon and the results once more challenged the expectations of planetary scientists. Instead of a dead, cratered world, the spacecraft found a surface every bit as exciting as Pluto's. Charon has a dark red northern polar cap, and this is probably material that has escaped from Pluto's atmosphere. Running along its equator is a vast canyon system nearly 1,600km in length. What could have caused this enormous fracture?

Names from science fiction are given to features here and the aptly named Vulcan Planum is, as Mr. Spock would say, fascinating. There is surprisingly little cratering on this plain, which indicates that some sort of resurfacing has taken place; the fingerprints of cryovolcanism in action. New Horizons was also able to image the other satellites, although Nix was the only other moon close enough to show interesting surface details. The spacecraft showed a red patch on the surface similar to the dark coloration found on Pluto and Charon.

The continuing mission

Although the Pluto flyby has long since passed, New Horizons is far from finished. The mission has already been a spectacular success and it has transformed an object that was once just a pinprick of light on a photographic plate into a complex and diverse world.

The discovery of mountains and apparent ice floes shows that even out here, in the frozen extremities of the Solar System, geological activity is quite common. Like the satellites of Jupiter and Saturn, Pluto and Charon remind us that we were wrong to write them off as dead, airless worlds.

No doubt in years to come the next generation of planetary scientists will use data from New Horizons to formulate new models of these distant wanderers. In the larger picture they will help to provide a better understanding of the early Solar System. I would imagine there will be many more surprises in store as the story of Pluto embarks on a new chapter.

LIFE ON PLUTO

The dwarf planet's subsurface oceans are a well of possibility.

It is currently believed that under the thick icy surface of Pluto there is a vast layer of water-ice. Beneath this lies the core of Pluto, containing radioactive elements that would release heat as they decay, thawing the water-ice above. Indeed, there may have been enough heating to have produced yet-undiscovered subsurface oceans on the dwarf planet.

Data from New Horizons indicates that Sputnik Planitia is probably an impact basin formed when a large object collided with the surface. As a result of the collision, water from this subsurface ocean could have welled up to produce the vast glacier we see today. One can't help wondering whether conditions in the subterranean oceans of Pluto were ever right for life to have got started.

ABOUT THE WRITER
Paul Abel is an astronomer at the University of Leicester. He co-hosts BBC Sky at Night's Virtual Planetarium every month.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Catching the Milky Way's Monsters

A revolution that began with colliding neutron stars is taking place in astronomy. Will Gater looks at how electromagnetic and gravitational wave observations are expanding our view of the cosmos.

The "Nessie" infrared-dark cloud observed by the Spitzer Space Telescope. By NASA/JPL/SSC Public domain, via Wikimedia Commons

A brave trio of astronomers based at Harvard's Center for Astrophysics have been monster hunting in the Milky Way. Their first discovery was 'Nessie'; not a creature from the depths of a Scottish loch, but rather a long, dark filament slashed through our Galaxy's disc. The structure, made up of a long thread of relatively dense gas whose sinuous turns reflect those of the monster 'seen' in the classic photo, is hundreds of lightyears long.

When I first heard about it, I thought the existence of such a structure was just a curiosity, but this 'Nessie' is a complicated beast. Understanding how such a filament could have formed, and how it has resisted being ripped apart by the turbulent structure of the Galaxy's gas clouds, is not easy. A proper survey is needed and others have set out on this quest before. Six separate papers have tried to compile catalogues of giant filaments, using data from infrared and radio surveys within which dense clumps of gas stand out. Some inspected their data by eye while others used algorithms and machine learning to look for long filaments, so the first task for Catherine Zucker — the PhD student leading this monster hunt — was to bring these different datasets together in a useful way, using data from ESA's Herschel observatory to measure their properties.

The results of her and her team's hard work are fascinating. There are, it turns out, several types of monsters lurking in the Milky Way. While all share a habitat — closer to the center of the Galaxy than we are, and close to the middle of the disc — there are distinct differences. The most obvious bear similarities to how we imagine the Loch Ness Monster to look: they're long, thin filaments that, thanks to a significant fraction of dense gas, appear capable of forming massive stars (in some, three quarters of their gas is dense enough to be able to form stars). Such large and thin features are almost certainly the result of gravity working on a grand scale. What's more, these giant filaments may be very important, acting like bones to underpin the whole spiral structure of the Milky Way.

The second type, which have less dense gas and a more rounded appearance, may be squeezed versions of normal molecular clouds, which form the bulk of the Milky Way's star-formation regions. A comparison with recent simulations suggests that this idea is at least plausible, though more work — probably with more powerful computers — is needed. The third and final type sits between the previous two; these are as thin as the 'Nessie' filament but contain relatively little dense gas. They seem to be networks of molecular clouds, sorted into a regular pattern by gas collapsing in a particular way, specifically due to something called a 'sausage instability' (a wonderful technical term).

The three types of filaments seem to tell different stories about how gas collapses locally and how the large-scale structure of the Milky Way is put together. In corralling all of these beasts in the same place, Zucker and her team have done a great service to those who'll follow and continue our exploration of the Milky Way's wild places.

ABOUT THE WRITER
Chris Lintott is an astrophysicist and co-presenter of The Sky at Night on BBC TV. He is also the director of the Zooniverse project.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Ripples, Radiation and Revelation

A revolution that began with colliding neutron stars is taking place in astronomy. Will Gater looks at how electromagnetic and gravitational wave observations are expanding our view of the cosmos.

By ESO (https://www.eso.org/public/images/eso0917a/) [CC BY 4.0], via Wikimedia Commons

Every so often, a true moment of scientific insight comes along, a moment that has a profound impact on how we explore the Universe. One such moment came in 2015 with the first detection of gravitational waves — ripples in the fabric of space-time that propagate from moving celestial bodies and violent events such as the merging of two black holes or neutron stars.

But despite the astronomical possibilities gravitational waves grant us, it was another, more recent, observation that opened up a new field of space science. That new field is multi-messenger astronomy, in which the secrets of the Universe are revealed through detecting and observing not only electromagnetic radiation, but gravitational waves and other celestial phenomena too. And its story begins around lunchtime, in August last year.

At 12:41 UT on 17 August 2017, the Laser Interferometer Gravitational-wave Observatory (LIGO) detectors in Washington and Louisiana, USA, sensed a gravitational wave washing over their respective sites. What happened next would thrill researchers and set off a dramatic chain of events.

Mere seconds later, in space, NASA's Fermi Gamma-ray Space Telescope and ESA's International Gamma-Ray Astrophysics Lab (INTEGRAL) satellite both caught a burst of gamma rays emanating from somewhere in the southern celestial hemisphere. Could the two things be related?

"Less than a minute after the gamma-ray [burst] was picked up by the Fermi team, they notified everyone else that they'd seen something interesting and gave a rough sky map of the location," recalls Dr. Michalis Agathos, a LIGO-Virgo Collaboration researcher based at the University of Cambridge.

The scramble to correlate

As news of the gamma-ray burst started to reach astronomers around the world, the LIGO researchers were already analyzing the wave their detectors had sensed, which they'd now catalogued as GW170817. Like the Fermi and INTEGRAL teams, the LIGO researchers notified collaborators at astronomical organizations around the world with access to telescopes observing across practically the entire electromagnetic spectrum.

Astronomers and gravitational wave researchers have started to work together like this in recent years in the hope of observing electromagnetic radiation (be it visible light, radio waves, X-rays or gammarays) from the events that trigger gravitational waves and send them rippling across the cosmos. Such an observation of electromagnetic radiation had never been made alongside a gravitational wave before but now, with GW170817, the LIGO-Virgo team worked with great urgency to notify their colleagues who had spotted the Gamma-ray burst.

"We already knew that the Fermi team had circulated [news of the Gamma-rays] so everyone at LIGO worked hard to get [details of GW170817] out fast with as much accurate information as possible," says Agathos.

Using data from a third detector, Virgo in Italy, the researchers were able to narrow down the area of the sky that GW170817 had come from. "When we cross-checked our sky map with that of Fermi, which was relatively wide but still narrowed down the location to a few hundred square degrees, we noticed a significant overlap. That encouraged people to believe that this was something that may be picked up by other telescopes," says Agathos.

On the ground, the professional observatories in Chile slewed towards the area specified by the LIGOVirgo team, picking out a new pinprick of light in NGC 4993, a galaxy around 130 million lightyears away. Meanwhile in orbit, both the Hubble Space Telescope and NASA's Swift satellite spotted it too, while the Chandra X-ray Observatory would later detect X-rays streaming from the same location. One estimate from the European Southern Observatory suggests that around 70 observatories saw the glowing dot that had appeared in the distant galaxy. More significant than the large number of eyes on the new spot of light, however, is what the diversity of observations constituted.

For the very first time, researchers had caught both electromagnetic radiation and gravitational waves emanating from an astronomical phenomenon. And with the data they'd amassed, the science of multimessenger astronomy — of studying distant celestial objects by examining more than just the light they emit — took a vast leap forward.

As had long been hoped, decades of technological improvements had brought gravitational wave detection to the point where it could work in concert with all kinds of observatories to provide astronomers with a new way to scrutinize astrophysical processes. And nowhere was this better demonstrated than in the revelations that came from the analysis of the GW170817 event.

Looking beyond the wave

"The data that we see in [a] gravitational wave detection is in a waveform," says Agathos. "You can see it as a wave that evolves in a certain way and the structure of it gives you information about the source that generated it."

Analysis of the GW170817 gravitational wave suggested that the event which had produced it was a violent collision between two neutron stars that had been spiraling in towards each other. When the two stars finally collided, the force of the impact shuddered the fabric of space-time, sending the gravitational wave rippling across the cosmos. It also illuminated their host galaxy with a powerful blast of radiation — the light the world's telescopes picked up in August.

The identification of a neutron star binary system as the origin of GW170817 was important in itself. The initial flash that the Fermi telescope saw was a phenomenon known as a short gamma-ray burst. Short gamma-ray bursts had been observed many times prior to the GW170817 event and one of the theories that astronomers had put forward for what causes them was the merging of neutron stars.

With Fermi's observation of the short gamma-ray burst and a simultaneous detection of a gravitational wave produced by a collision of neutron stars, astronomers now had a key piece of evidence to support that theory.

The kilonova question

This revelation from the study of the GW170817 gravitational wave was the first triumph of multimessenger astronomy, but it wasn't the only one. The telescopes observing the electromagnetic radiation from the explosion caused by the two neutron stars colliding were able to capture spectra of the event. In doing so they were able to shed light on one of the great enigmas in astrophysics: where some of the heaviest elements in the Universe come from.

"Once you have the spectrum you can infer things about the [chemical] composition of the matter that you're observing," says Agathos. "The fact that we saw spectral lines of certain elements in this detection indicated that a big portion of elements, such as gold, platinum, uranium or other heavy elements, [are] actually produced in this type of process. This had been an open question for decades."

Those heavy elements were flung out by the explosion observed by the follow-up telescopes &mash; a powerful blast known as a 'kilonova', which astronomers had for many years suspected would occur when two neutron stars smash together. Kilonovae are fainter and release less material than supernovae, but as they dim rapidly they're much more tricky to catch.

"Sometimes you can see objects that have characteristics which would have looked like the theoretical models put forward for a kilonova," says Dr Kate Maguire, an expert in supernovae from Queen's University, Belfast. "But because they fade away very quickly from their brightness we never had good datasets."

Indeed, the multi-messenger nature of the GW170817 observations was crucial to positively identifying it as the kilonova predicted by models. "This is the first object that's conclusively a kilonova, because we have the gravitational wave detection of the two neutron stars merging," adds Maguire.

More messages

Astronomers hope to make more multi-messenger observations of kilonovae in order to get a better understanding of these events. But future multimessenger astronomy studies may also offer new insight into their more energetic cousins, supernovae, as well. And that's because there's another type of 'messenger' to pick up, a messenger that wasn't detected in the GW170817 event but one that could reveal the inner workings of these violent stellar detonations: neutrinos.

Neutrino particles can be produced in the powerful core-collapse supernovae that occur when a massive star dies, but they're extraordinarily hard to detect and require specialist detectors, such as the IceCube Neutrino observatory located at the South Pole. "We've only seen neutrinos from one supernova, 1987A, and that was 20 neutrinos out nos [a theorized total of] 1058," says Maguire.

Nevertheless if a supernova went off in the Milky Way and enough neutrinos could be detected from the blast, along with gravitational waves and electromagnetic radiation, it would be a pivotal observation. "The neutrinos would tell us about the explosion mechanism of the core-collapse supernova," explains Maguire. "The gravitational wave detection would be very nice for tying down the properties of the system, such as the mass. And we'd have the electromagnetic radiation as well — because it would be a supernova in our galaxy we'd be able to get very detailed observations. It would be incredibly exciting if we were able to do that."

With LIGO coming back online later this year, professional astronomers will be preparing to jump into action when another gravitational wave signal is detected. But there's another development on the horizon that should excite amateur astronomers too. In the future, the private notifications that the LIGO team send out to collaborators alerting them to a potential new gravitational wave event will be made more widely available.

"One cannot exclude the possibility that certain sources may be observable by amateur astronomers with decent telescopes," says Agathos. "For instance the host galaxy of the first neutron star binary [merger] detection was something in the region of [mag.] +12.4 and the source itself was not much dimmer. With a decent telescope, if you're lucky enough and you're in a place where the sky is dark and clear, you may actually be able to discover things before the large telescopes do."

The future of multi-messenger astronomy will certainly involve advanced, professional observatories and rapid-reaction, wide-field telescopes working alongside gravitational wave and neutrino detectors. But in among the authors of forthcoming studies they produce, we may well also see the names of dedicated amateurs working from their own back gardens.

ABOUT THE WRITER
Will Gater is an astronomy journalist, author and presenter. Follow him on Twitter at @willgater or visit willgater.com.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Spying on the Neighbors

Hubble's successor, the James Webb Space Telescope, will look farther back in time and space than ever before. But this giant telescope could also be turned to targets right in our own cosmic backyard, as Benjamin Skuse reveals.

Creative Commons Zero (CC0) license

Bigger and more powerful than any space observatory ever launched, the James Webb Space Telescope's (JSWT's) infrared gaze will stretch to the very first stars and galaxies being born, offering new insight into the Universe's origins. Its eyes will also scan exoplanets in the search for the building blocks of life beyond our cosmic doorstep, looking for answers to the perennial question: 'Are we alone?'

What many do not realize though is that JWST will not solely be peering at the farthest reaches of the Universe. In fact, with some clever reconfiguring, Webb will be able to cast its spying eye on our closest cosmic neighbors, hoping to uncover some of the secrets hidden within our Solar System.

Adapting JWST for the local nature of Solar System science, however, is fraught with difficulties. The biggest is that the telescope is designed for detecting the faintest, most distant objects. Its extremely sensitive sensors therefore need to be protected at all times from the overpowering light and heat from the Sun, which is why it is equipped with a tennis court-sized sunshield. This would not be a problem but for the fact that Webb will be located at the second Lagrangian point (L2), some 1.5 million km beyond Earth's orbit. As it is, the sunshield permanently shrouds Mercury, Venus, Earth and the Moon from Webb's gaze.

The closest of our neighbors Webb will be able to track are near-Earth objects (NEOs) like Eros and Halley's Comet. "The Earth's atmosphere makes it very difficult to observe NEOs in certain wavelength regions, some of which are very informative and diagnostic of things like water and organics," says NASA research scientist Cristina Thomas. "If we want to focus on origins of life questions, then going outside the atmosphere helps us."

The brightness dilemma

The second nearest target, Mars and its moons, will only be within JWST's spyglass every two years. Webb will add an infrared view to the Mars toolbox of rovers and satellites tasked with studying the planet and its potential for hosting life.

NASA planetary scientist Geronimo Villanueva believes this capability will be invaluable: "JWST will open a new window into the planet's current and past habitability," he says. Villanueva should know. Among other achievements, he was the co-discoverer of methane on the planet (a possible biosignature) and mapped deuterium to hydrogen ratios in Mars's atmospheric water — leading to the realization that the Red Planet had an ancient ocean. "New observations are urgently needed to confirm these findings," he says.

The Red Planet brings us to the second main challenge in using Webb to look over the garden fence: overexposure. Essentially, Mars is far too bright for the Webb's sensitive detectors to cope with. "Even Pluto is bright enough that if we took full-frame data with our widest filters it would saturate," says John Stansberry, a Space Telescope Science Institute (STScI) scientist. "So bright has a different definition for JWST!"

To get round this, NASA will command the instrument to just process a tiny square right in the middle of the full detector array. "Instead of having a 4-megapixel image, we'll take a much smaller postage stamp in the middle," says NASA space scientist Conor Nixon. "That way we can read that out really quickly before it becomes overexposed."

Beyond Mars is where JWST will really have to start getting busy. With an observing window of around 50 days approximately every six months, the giant planets Jupiter, Saturn, Uranus and Neptune will all be viewable, as well as their associated rings and 170 known moons.

While the planets themselves will be monitored by JWST, some of the most interesting science will concern their satellites. From helping to solve the tidal heating conundrum on Jupiter's moon Io to taking over the task of watching the Saturnian moon Titan after the Cassini mission comes to an end or even establishing whether Neptune's retrograde-orbit moon Triton has a subsurface ocean, JWST offers the chance to view and try to understand the most dynamic processes of the Solar System's satellites.

Focus on the small things

However, the bread and butter for JWST's Solar System science will be even less studied, smaller and distant bodies: comets, the main belt asteroids situated between Mars and Jupiter, the Trojan asteroids that share Jupiter's orbit, and the Kuiper Belt objects — including dwarf planet Pluto and the yet-to-be-seen Planet Nine. All could yield clues to how the Solar System came to be the home we know.

"Because they retain material from the very start of Solar System history, they reveal the chemical makeup of the planets and how planets form," says Andy Rivkin, planetary astronomer from Johns Hopkins University.

For these smaller distant bodies and ring systems, NASA has another trick up its sleeve: stellar occultations, where a star is temporarily blocked by a passing Solar System body.

"If you can take data very quickly as an object passes in front of a star, you can measure various things about the object itself," explains Stansberry. By looking at the changes to the star's light as it disappears behind a planet, Webb will be able to look at ring microstructures, and may discover rings around minor planets or even find atmospheres around various Kuiper Belt objects.

All of these proposed targets for Webb suggest the Solar System's most well-hidden mysteries may soon be solved, but one paper really sticks out as having the potential to captivate the public's imagination. In it, the authors propose using JWST and Hubble together to create stereo 3D movies of the planets and moons amateur astronomers have been fascinated by for centuries.

"I worked with a vision scientist colleague to understand the limits of human depth perception," says Joel Green, a project scientist at STScI, who led the study. "It turned out that if you had eyes one million miles apart, and the resolution of Hubble and Webb (roughly 1,000 times better than 20/20 vision), you could actually see objects like Mars, or Jupiter's moon system or Saturn's rings in stereo 3D!"

Not only might this be a boon to astronomers, offering stereo data on weather changes, collisional studies, ring system shocks, and many more, but would also be a first for science education, making ancient astronomical bodies come to life in the classroom. As Green notes: "These are the sorts of images that could inspire a generation."

ABOUT THE WRITER
Dr. Benjamin Skuse is a mathematician turned science writer based in Bristol, UK.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Grand Designs

Grand Canyon National Park is set to get a whole lot darker as it embraces its International Dark Sky status, writes Jamie Carter.

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For anyone after an uplifting experience from nature, the Grand Canyon almost has it all. By day you can stand anywhere along its South Rim and peer down nearly 2,000m into its layer-cake bands of red rock, taking you back two billion years into Earth's deepest history. When the Sun goes down, the combination of a high elevation and dry desert air means clear, cloudless night skies are common. So why doesn't the Grand Canyon National Park have a particularly high reputation among amateur astronomers and astrophotographers?

Five million visitors per year, that's why. Most of them visit Grand Canyon Village on the South Rim, which is easily accessible from Flagstaff in Arizona and only a few hours from Las Vegas in neighboring Nevada. Over the years the undeniably picturesque properties on the South Rim added lighting. And then more lighting. Even the pathways along the rim were floodlit.

This wilderness gateway is now a major light polluter, but that's all set to change in the wake of the June 2016 announcement that the reserve has been provisionally designated as an International Dark Sky Park. This certification is awarded by the International Dark-Sky Association (IDA), a US-based organization that encourages others to maintain the darkness of the night sky for future generations.

The 'provisional' status reflects the complex job ahead. There are thousands of light fixtures on both rims and within the canyon itself, and the National Park Service has set a deadline of June 2019 — the park's centenary year — to retrofit two-thirds of them to comply with the IDA's lighting guidelines.

Harking back to darker times

"Technology is coming along nicely, with excellent night sky and eye-friendly choices now on the market, with prices that are becoming competitive with more common fixtures and bulbs," says Jane Rodgers, deputy chief science and resource management at Grand Canyon National Park, who applied for the Dark Sky Park status. "Backpackers and campers within the canyon will look up at the South Rim and see fewer, more subdued lights, most of which are illuminated only for a few hours after sunset and an hour or so before sunrise. The general aesthetics will hark back to the time when the village was first developed, where the natural world dominated and visitors experienced the feel of an amazing night sky."

Not that the national park doesn't already promote itself as a dark-sky destination. Its rangers are well informed about the night sky, and a star party has been held here each June for over a quarter of a century. Last year's even included talks in the visitor center, constellation tours and free telescope viewing outside the building and at nearby Mather Point, a 10-minute walk away on the rim.

The north-south divide

At other times of year (May to September pretty much guarantees a dry climate and crystal clear night skies), there are night-time walks and talks by rangers, who often set up a telescope for public use. Amateurs and professional astronomers from nearby Lowell Observatory in Flagstaff (where Clyde Tombaugh discovered Pluto) make visits, while on the darker North Rim, the Saguaro Astronomy Club of Phoenix set up telescopes on the porch of the Grand Canyon Lodge.

Mather Point is the best place for stargazing on the South Rim, though Rodgers is looking into establishing a designated night-sky viewing area. Nearby Hermit's Rest and the many pullouts on the flat Rim Trail are perfect, as are the remoter Desert View and Lipan Point on the South Rim, about 30km drive from Grand Canyon Village.

Alternatively, pitch a tent in one of the reserve's campgrounds. Here you may well find a ranger who can point out the local Navajo tribe's giant constellations: the First Revolving Male, First Revolving Female and the Central Fire. You'll recognize them; they're based on the Plough, Cassiopeia and Polaris, respectively. The constantly turning circumpolar stars represent the Navajo ideal home of a husband, a wife and an abode. By protecting natural darkness as well as the natural landscapes, Grand Canyon is itself committing to a beautiful billion-year marriage all of its own.

ABOUT THE WRITER
Eclipse-chaser and dark skies expert Jamie Carter is the author of A Stargazing Program for Beginners: A Pocket Field Guide

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Capturing the Hunter

The familiar winter constellation of Orion holds many surprises for imagers who want to delve a little deeper, says Will Gater.

Photo taken by astrophotographer Steve Peters at Fremont Peak, California.

There are few constellations that grab the attention quite like that icon of the winter heavens, Orion. The glittering bright stars, the instantly recognizable 'belt' and the many glowing nebulae scattered within the Hunter's boundaries all make Orion a wonder to behold on a frosty, dark night. But the constellation is also a rich hunting ground for astrophotographers seeking captivating targets of many kinds. In this article we're going to explore some of the different ways Orion's splendors can be captured on camera, from a simple nightscape that conveys the naked-eye view to advanced CCD imaging techniques that can reveal the constellation's extraordinary deep-sky features. And hopefully, by the end of this piece, you'll agree with us that no matter how many times you catch sight of the Hunter, you'll always find something new to inspire you and test your astrophotography skills.

The Hunter in his element

Experience Level: Beginner to Intermediate
What You'll Need: A DSLR or bridge camera and a sturdy photographic tripod. A wide kit lens (of the kind that comes with most DSLRs) will be perfectly sufficient. More experienced astrophotographers may also want to use a portable tracking mount to capture longer exposures.

There's something tremendously evocative about glimpsing the bright stars of Orion over a wintery landscape — or towards the end of the autumn months just as the nights start to get longer and colder — so in this project we're going to look at how to shoot a 'nightscape' that attempts to capture some of that magic.

STEP 1: Make a conceptual plan
Thinking about the emotions you want to convey or elicit with your shot can help you to plan a powerful picture, and it'll inform every stage of the photographic process. For example, if you wanted to evoke the harsh iciness of winter observing you might shoot Orion over an isolated, leafless tree in a barren landscape, and process in such a way as to create a hard contrast between land and sky.

STEP 2: Select your focal length or a prime lens
Once you've thought about what atmosphere you want to capture with your image, you can select the focal length you'll be shooting at. A typical kit lens set to around 24mm, or an equivalent prime lens, provides a wide field of view for Orion on a camera's sensor, allowing you to fit in the brighter central stars and the Hunter's fainter outlying 'arms'.

STEP 3: Focus the view
Next focus the view. Some cameras have a live preview function that can be zoomed onto a suitable star, giving you instant feedback as you make slight focusing adjustments. With Orion there's no shortage of bright stars that can be used for this. Repeat the process a few times — checking that the star is a small as possible — so you're certain the image is as sharp as it can be.

STEP 4: Compose with the landscape and sky conditions
To compose your nightscape you can take short, very high ISO test exposures to show you the balance and positioning of foreground and sky, and any structures or landscape features in frame. Try to use the foreground — trees, buildings, etc. — to lead the viewer's eye toward Orion. Sometimes clouds can be used as a framing device too, and thin cloud can even 'bloat' and enhance the colors of bright stars.

STEP 5: Set the exposure length, aperture and ISO
When shooting, keep the lens aperture wide open (lowest f-stop), though some lenses will perform better when reduced a few stops. Experiment with the ISO and exposure length until you're happy with the look. You may need to use an exposure that very slightly trails the stars in order to define the foreground.

STEP 6: Process your image
When processing nightscapes, reducing the noise in the image and bringing out foreground detail are the main challenges; as long as you shoot in RAW format, modern image-processing software is well-equipped to handle these tasks. In Photoshop or GIMP you can correct the color balance, and use the 'Curves' tool to bring out star fields and improve overall contrast and definition.

Far and Wide

Reveal the hidden delights lurking within Orion with the help of long-exposure, wide-field imaging.

Experience Level: Intermediate
What You'll Need: A DSLR, a tracking mount and either a relatively long focal length camera lens (between 100 and 300mm focal length on a full-format DSLR) or a short focal length refractor. You could use a CCD camera, but the field of view produced by your setup will need to be at least 5° across or you'll need to mosaic.

One of the things that makes Orion so attractive for astrophotography is the diversity of deep-sky objects within its borders, from pinkish-red star forming regions to blue-tinted reflection nebulae.

The proximity of these targets to one another means that long-exposure wide-field imaging of Orion can produce some spectacular compositions. Not only do such wide-field images show the positions of objects such as the Orion and Horsehead Nebulae in relation to one another, but they can also reveal the rarely seen fainter surroundings of objects that are usually given the 'close-up' treatment, such as the aforementioned nebulae.

A DSLR with a long focal length lens and mounted on some form of equatorial tracking mount is probably the simplest setup with which to get started in wide-field imaging. Unlike most deep-sky imaging, wide-field deep-sky astrophotography generally doesn't require auto guiding, as it's possible to capture good data with unguided sub-exposures of just a minute or two.

With fast prime lenses and those relatively short exposure lengths, you may be surprised at how easily you can pick up some of Orion's most recognizable deep sky objects. For the best results capture multiple sub-exposures (as well as dark frames and flat fields) and then calibrate and stack them, using software such as the free DeepSkyStacker, before final enhancements in your preferred image processing software.

Colorful captures

With the right setup you can show Orion is more than just white stars against a black background.

Experience Level: Beginner

What You'll Need: A basic DSLR or bridge camera fitted with a lens that allows manual focusing (some compact digital cameras will also work depending on the lens/focusing mechanism they use). You'll also need a photographic tripod and your camera will need to be able to take exposures of a few seconds.

The color variation of Orion's bright stars is one of the most captivating things about the constellation, yet it can be tricky to capture these wonderful hues as the chromatic aberration in some camera lenses overwhelms the true star color. One method for showing the tints of stars such as Betelgeuse, Rigel and W Orionis is to manually defocus the image. It's a technique that was made famous by the renowned astrophotographer David Malin many years ago. You can use this method with a wide lens (or a fast long lens) on a static tripod, as long as you use short exposures — a second or so in the case of a longer lens. All you do is frame the star (or constellation), defocus the lens a little by hand and capture an exposure, usually at a mid-to-high level ISO setting. In the two composite images below we focused on Betelgeuse and Rigel. We captured a number of exposures and in between each one we defocused the lens a bit more. Then we combined them into one frame using processing software. It's a very artificial composition, but it does give a flavor of one of the things that makes observing and imaging Orion special.

Portrait of a stellar nursery

Capture the Orion Nebula's ethereal pink swirls of gas and dust that are giving birth to new stars.

Experience Level: Intermediate to advanced
What You'll Need: A small refractor or Newtonian telescope carried on a motorized tracking mount, plus a monochrome CCD camera (and a computer to control it) with a set of LRGB imaging filters and a filter wheel. For exposures of more than a few minutes it's also a good idea to use an autoguiding system alongside the above, though this is not absolutely necessary.

There are few greater tests of a deep-sky astrophotographer's skills than the magnificent Orion Nebula, M42. Among the many challenges it provides are the faint outer regions of the nebula that can be lost in processing, or simply not picked up at all during the imaging process, and its dazzlingly bright core that requires careful planning to capture. In the step-by-step guide below we've described the basic process of how to go about shooting M42 with the kind of setup you might typically have if you're starting out in CCD imaging — that is a monochrome CCD camera and a set of LRGB filters (luminance, red, green and blue) with which to make a full-color image.

STEP 1: Set up and polar align accurately
Once you've got your equipment set up, spend some time finessing the polar alignment of your mount. This is so you'll be able to get the longest unguided exposures your mount is capable of before the stars drift out of position — this is especially important if you're not using autoguiding equipment.

STEP 2: Capture different length luminance exposures
Use short, 'binned', test exposures to compose the image. Then take three groups of exposures through a clear luminance filter: short ones for M42's bright core, longer ones for the main body and, for the faint outer regions, as long as your unguided mount can manage without the stars 'wandering' (usually several minutes).

STEP 3: Get the RGB color
When you've got around 10-15 sub-exposures for each of the three groups of luminance data, you can move on to capturing the color data through red, green and blue filters. Capture at least 10-15 images per color channel — aim for an exposure length similar to your shots of the main body of M42 with the luminance filter.

STEP 4: Take dark frames and flat fields
After capturing each 'LRGB' channel, carefully stretch a clean white pillowcase or t-shirt over the scope aperture (without touching the lens) and illuminate it with a torch before taking an image. This is a flat field, which records image artefacts such as vignetting and dust on the optics. Also take a set of dark frames if the data from your CCD needs them.

STEP 5: Stack and calibrate the data
You should now have six sets of sub-exposures: three luminance groups of varying exposure length and one for each of the RGB channels. Load them into your preferred astronomical image processing software (for example, DeepSkyStacker) and use the flat fields and dark frames to calibrate them before stacking those calibrated sets into six images.

STEP 6: Combine the three luminance images
Bring the three luminance images into layers-based image processing software, such as Photoshop or GIMP. With each image in a separate layer, erase the overexposed portion of the long-exposure image so that the 'main-body' exposure shows through — do the same for the main body layer so the core shows clearly. Merge the layers.

STEP 7: Add the color and make final processing adjustments
Next, place your red, green and blue filtered images in their respective color 'channel' in a new image file. Copy the resulting full-color image, as a separate layer, into the luminance file created in Step 6 and turn its blending mode to 'Color'. Lastly make any final image tweaks to your taste.

ABOUT THE WRITER
Will Gater is an astronomy journalist, author and presenter. Follow him on Twitter at @willgater or visit willgater.com.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Mission to Mercury

October will see the launch of a European mission to the innermost world in our Solar System.

By NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington [Public domain], via Wikimedia Commons

"A peculiar planet of mysteries and surprises" — this is how European planetary scientist Johannes Benkhoff describes Mercury. In October this year, ESA will launch the BepiColombo spacecraft to the Solar System's smallest and innermost planet. Some eight years from now, it will begin studying Mercury in meticulous detail across the electromagnetic spectrum. According to Benkhoff, the mission's project scientist, planetary researchers expect BepiColombo to solve many Mercurial mysteries. It's a planet, he says, that is also a key element in understanding the formation of the Solar System.

The mission's Ariane 5 rocket launch from French Guiana will send two orbiters to the planet: the relatively small Japanese Mercury Magnetospheric Orbiter (MMO) and ESA's 4,100kg Mercury Planetary Orbiter (MPO). Both are mounted on a six-meter tall transfer module that will deliver the two craft into orbit around the 4,879km-diameter planet.

"It's a very harsh environment," says Benkhoff, referring to Mercury's distance from the Sun, which varies between just 46 and 69 million km. "But if we're lucky, the nominal mission duration of one year may be extended up to four years."

Although Mercury is much closer to Earth than, say, Saturn, it's tough to get there, basically because the planet's orbital speed is much higher than Earth's. The first Mercury probe, NASA's Mariner 10, didn't even make it into orbit. Launched in 1973, it performed three close flybys in 1974 and 1975, before ending up orbiting the Sun. Mariner 10 mapped just shy of half of the planet's surface, revealing a crater pocked landscape. It also discovered a weak magnetic field: quite a surprise, since no one expects Mercury to have retained a molten core.

It would be 30 years before another probe set course for Mercury. NASA's MESSENGER spacecraft launched in August 2004, and orbited the barren world between March 2011 and its intentional crash in April 2015. From its polar orbit, MESSENGER collected nearly 290,000 images and mapped the planet's topography. Among other things, it discovered deposits of ice at the floors of permanently shadowed polar craters, mysterious 'hollows' beneath the surface, signs of relatively recent volcanic activity, and a mysterious displacement of the magnetic field by 400km northwards with respect to the planet's center.

So what's left for BepiColombo to discover? A lot, says former project manager Jan van Casteren at the European Space Research and Technology Center (ESTEC) in Noordwijk, the Netherlands. Originally, he says, BepiColombo was scheduled to arrive first, but the project was delayed by technological problems, cost overruns and redesigns. "Still, in 2009, ESA's Science Programme Committee decided to give the go-ahead for the mission because of its great scientific potential. BepiColombo is a much more versatile mission than MESSENGER, which was relatively simple."

No easy journey

During its seven-year cruise phase, BepiColombo's solar orbit will gradually be tweaked by one Earth flyby, two Venus flybys and no less than six Mercury flybys. This 'gravity assist' technique, pioneered by Mariner 10, was invented by Italian astronomer Giuseppi 'Bepi' Colombo, after whom the mission is named. The craft's versatile ion engine will perform additional orbital corrections. Eventually, in early December 2025, BepiColombo will arrive in its elliptical polar orbit. A few months later, the lowest point of the orbit is brought down to just 250km, and science operations will begin.

At Mercury, a spacecraft receives about 10 times more solar energy than it would in Earth orbit: some 14,500 watts per square meter. Moreover, Mercury's surface is so hot (430°C) that BepiColombo's main orbiter needs to be protected from the planet's infrared radiation, which delivers more energy: 5,500 watts per square meter. To cope with these extremes, the craft is completely wrapped in thick, multilayer thermal blankets. A huge contraption of silver-coated titanium fins always points away from the planet to radiate excess heat away into space.

You might expect that the use of solar panels is straightforward when you're so close to the Sun, but you'd be wrong, as Markus Schelkle of Airbus Defence and Space in Germany (the spacecraft's prime contractor) explains. "The solar array had to be newly developed using novel materials," he says. "It's very difficult to make them resistant to both high temperatures and strong ultraviolet radiation." The same is true for the large solar arrays on BepiColombo's transfer module, which provide the energy for the ion engine. "Developing the solar arrays took as long as developing the whole spacecraft," says Schelkle.

As the MPO studies the planet up close, the smaller MMO will monitor the solar wind, the planet's magnetic field and the extremely tenuous sodium-rich 'exosphere'. Because of strong solar wind buffeting, Mercury's magnetosphere can sometimes be pushed back all the way to the surface. As a result, the solar wind directly interacts with the surface, possibly releasing sodium atoms in the process. "It's one of the questions we want to answer," says Hajime Hayakawa of the Japanese space agency JAXA. Another big issue he hopes MMO will solve is the mysterious 'shift' of Mercury's magnetic dipole. Meanwhile, as project scientist Benkhoff recounts, the MPO will map the elemental and chemical composition of the planet's surface, look for morphological changes in the mysterious subsurface 'hollows' (which may be due to the loss of volatiles), hopefully elucidate the origin of the polar ice deposits and study the planet's relatively large iron-nickel core. "Also," says Benkhoff, "Mercury's potassium/thorium ratio is much higher than current planetary formation models predict. The mission may shed new light on the origin of the Solar System." Van Casteren is confident that the ambitious €1.65 billion mission will be worth every penny. "The highest resolution images will reveal details as small as 5m," he says, "and BepiColombo has an impressive suite of 11 science experiments. It would have been nice to be the first, but in the long run, it's the science that counts."

TARGET MERCURY

Why is studying Mercury so tricky, and what might we learn from doing so?

Mercury is the smallest and innermost planet in the Solar System. Studying it from Earth (or with an Earth-orbiting instrument like the Hubble Space Telescope) is difficult, because it always appears close to the Sun in the sky.

Because Mercury is orbiting the Sun so fast (48kms on average), a spacecraft launched from Earth has to undergo a large change in velocity to end up orbiting the planet. That's one reason why there have been so few Mercury probes so far.

Visible light, X-rays and ultraviolet radiation from the Sun are about 10 times more powerful at Mercury than they are on Earth. The solar wind (charged particles from the Sun) is also more energetic. This is another reason why Mercury has remained relatively unexplored.

Compared to the other terrestrial planets, Mercury has a very large iron-nickel core. No one knows why. Maybe a huge primordial impact blew away most of its rocky mantle. Or maybe scientists need to adapt their pet theories on the formation of the Solar System.

Learning more about Mercury and its extreme environment will also help in understanding habitable-zone exoplanets that orbit at comparable distances to their parent dwarf stars.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

The Three Types of Twilight

The period between 'day' and 'night' is complex, and so is the sky at this time.

By Pmurph5 (Own work) [CC BY-SA 4.0], via Wikimedia Commons

The changes that occur during dusk can be as striking as anything we observe in nature. Everything we can see changes, as the brightness of the sky drops to less than 3/10,000ths of a per cent of its intensity at sunset. Yet this daily spectacle is often lost to us, perhaps obscured by cloud, but also obliterated by artificial lighting and sometimes simply ignored because of its regularity.

Twilight is not a single, fixed state, but a gradual change that has three distinct phases. The first is civil twilight, which begins as the upper limb of the Sun disappears below the horizon and ends at civil dusk, when the geometric center of the Sun is 6° below the horizon. During this period, you can carry on doing things much the same as if the Sun were above the horizon, lit only by the still-blue overhead sky. The first half an hour being dubbed by photographers as the 'blue hour'.

We tend to look to the west at sunset, drawn by the coral pink hues above the horizon, and miss the more dramatic changes that are happening behind us. Here, we see a band of more muted amaranth pink, dubbed the Belt of Venus, illuminated by red sunlight that is not scattered in its passage through the atmosphere. Below is a rising purple swathe, that part of the visible sky that is in Earth's shadow. During civil twilight, only the very brightest stars and planets become visible.

Civil dusk signals the beginning of nautical twilight, which persists until the geometric center of the Sun is 12° below the horizon — nautical dusk. At nautical dusk, it's sufficiently dark that a sailor at sea would not be able to see the horizon, hence its name. Our monochrome scotopic (low light) vision begins to dominate and colors fade as everything on land takes on shades of grey. The purple in the east merges with darkening sky above. First-magnitude stars begin to appear. Initially they seem lonely points of light, but they gradually multiply as the sky darkens and fainter stars join them. Eventually, the entire Plough asterism in Ursa Major appears, pointing to Polaris, so at last we can polar align our equatorial mounts. Night is approaching, but the sunlit sky is still visible on the sunset horizon. The third phase, astronomical twilight, is beginning.

Light's last gasp

As the Sun descends past nautical dusk and into astronomical twilight, when our star is between 12° and 18° below the horizon, its illumination is replaced by other sources. For too many of us, this is the skyglow from artificial light, but even in unlit places on a Moonless night the sky is never completely dark. The combination of an imperceptibly faint auroral glow, the zodiacal light (sunlight reflected off interplanetary dust particles), and the light of diffuse matter in our Galaxy all contribute, though their contribution is less than that of a single mag. +6.5 star if it was distributed over an area the size of the Moon.

Astronomical dusk takes place when the Sun's geometric center drops to 18° below the horizon. Above our heads we will see, with dark-adapted eyes, objects as faint as we are likely to. Away from light pollution, the Milky Way shows structure sculpted by the dust of dark nebulae. The Andromeda Galaxy and the Double Cluster in Perseus may show themselves even without binoculars. The varied colors of stars become more apparent, and our awareness of the existence of artificial satellites and sporadic meteors grows. The glittering sky-dome above our heads appears to have come closer. This is night.

Then, all too soon, it is over. The sky brightens, the stars fade, the twilight phases play out in reverse. Dawn, and a brand-new day, is upon us.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Our Fortunate Earth

Our world would be a much more chaotic place if Jupiter's orbit was only slightly different.

This color image of the Earth was obtained by Galileo on Dec. 11, 1990. Image credit: NASA/JPL

One of the central questions in planetary science, and the possibility of life elsewhere in the cosmos, is how ordinary our own planet is. Is Earth in some way in a special situation, offering unusually clement conditions for the emergence of life, or are there potentially multitudes of planets in our Galaxy that could be alive? This question is becoming more and more important in light of the fact that we continue to discover extoplanets. What features would these far-flung worlds need to offer the best hope for harboring extraterrestral life, and therefore which candidates should we shortlist for our follow-up telescopic observations of their atmospheres to look for signs of biology?

In particular, it's been argued that Earth may have offered an especially stable climate over the billions of years of its existence. Earth's climate has varied over planetary history — from the hot and humid times of the early Triassic period 250 million years ago, to the 'Snowball Earth' episodes when much of the world is thought to have frozen over. But overall, the terrestrial climate has remained remarkably stable. Some of the main drivers for a fluctuating climate, seen over the past few million years of the world swinging between ice ages and warmer interglacial respites, are the Milankovitch cycles. These are cosmic cycles in the eccentricity of Earth's orbit (how circular or egg-shaped it is), the planet's obliquity (how much its axis tilts), and the timing of the seasons — all affected by the gravitational influences of the other planets in the Solar System. The orbital eccentricity of Mercury, for example, varies far more than that of Earth. So the key question is, if the architecture of the Solar System was slightly different, how would this affect our world's orbit?

Jonathan Horner, at the University of Southern Queensland, and his colleagues have explored just this. They used a computer model of the Solar System to track how Earth's orbital oscillations changed as they tweaked the orbits of Jupiter, Venus or Mars in the Solar System, trying almost 40,000 different situations for each planet.

The most obvious result of their simulations, although not entirely unexpected, is that if Jupiter was slightly closer to the Sun it would completely disrupt Earth's stable orbit. Similarly, moving Venus further out than about 0.92 AU spells disaster. Interestingly, though, they did find that Venus and Earth could be stable even with both orbiting at 1 AU if they were located in a 1:1 orbital resonance — just like the Trojan asteroids in a locked orbit with Jupiter. This is one possibility for habitable worlds in exoplanetary systems with warm Jupiters.

The most important results, however, are the ones looking at more subtle shifts to Earth's Milankovitch cycles and how these might affect the planet's climate. The team intend to apply their modelling approach to Earth-like exoplanets, as and when they are discovered. Any worlds likely to experience more pronounced climate variability could have a lower chance of maintaining life, and Horner says that these can be ruled out and our attentions instead focused on the more promising worlds.

ABOUT THE WRITER
Lewis Dartnell is an astrobiology researcher at the University of Westminster and the author of The Knowledge: How to Rebuild our World from Scratch (www.theknowledge.org)

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Imaging for Science, Asteroids

Pete Lawrence looks at how your images can help monitor the position of potentially hazardous objects crossing Earth's orbit.

This computer-generated image depicts the flyby of asteroid 2014 JO25. The asteroid safely flew past the Earth on April 19, 2017 at a distance of about 1.1 million miles (1.8 million kilometers), or about 4.6 times the distance between Earth and the moon. Image credit: NASA/JPL-Caltech

Asteroids or minor planets are small Solar System bodies that are visible because they reflect sunlight. The larger members of this group have dimensions measured in hundreds of kilometers, but asteroids can be as small as 1m along their largest axis. Most asteroids are located in what's known as the main belt, a huge repository for such objects located between the orbits of Mars and Jupiter. In all but very rare circumstances, asteroids appear star-like through amateur scopes. Visually, they can be measured in terms of their brightness, position and occasional apparent interactions with other objects.

The sheer number of asteroids in orbit around the Sun means that occasionally we get to see one occult a distant star. Asteroid occultations provide an important way to determine the shape profile of these rocky bodies.

Accurate date and time recording is vital when observing asteroids, as it is this information which ultimately is used to refine the objects orbit and position.

Asteroids look just like stars when viewed through a telescope. It's only when their positions have been noted or photographed over an extended period — normally days — that their motion and true nature is revealed. Most asteroids appear to move slowly against the background stars but those that venture close to Earth may have enough apparent speed to appear to move in real time when viewed through a telescope or binoculars.

Bodies that have orbits bringing them close to Earth are known as near-Earth objects (NEOs) of which near-Earth asteroids (NEAs) are a subset. NEOs larger than 140m that cross Earth's orbit are classed as potentially hazardous objects (PHOs) and again, asteroids form a subset known as potentially hazardous asteroids (PHAs). To date, all known PHOs are PHAs.

Scientific asteroid images for astrometry and photometry need to record the body as a sharp dot without trailing. For slow-moving asteroids this may not be an issue, but fast movers require short exposures or setups that track the asteroid itself. This is especially useful for the high-cadence photometry necessary to determine the light curve, and hence spin-rate, of an asteroid.

For more general appeal, in outreach material for example, a fast-moving asteroid provides a convenient way to produce a trail that would otherwise take many extended exposures to capture. In this instance, a correctly polar aligned telescope tracking at the sidereal rate or, better still, autoguided on the stars, will produce a sharp star field with the asteroid as a light trail. A similar effect can be created by aligning shorter exposures on the stars, and stacking them with the brighter elements set to show through.

Many asteroids are within range of a basic telescope and DSLR setup. For scientifically calibrated work, CCD cameras, (preferably with specialist filters) are recommended. By using planetary imaging techniques, larger telescopes may even be able to capture larger asteroids as extended discs during favorable oppositions, rather than the usual star-like dot.

Project 2: Asteroid astrometry

Use software to help you plot the exact position of small space rocks

Measuring the position of an asteroid is an important step in determining and refining its orbit. This is especially true for asteroids on eccentric orbits, which have the capacity to pass close to Earth. Smaller bodies returning to the inner Solar System may have been gravitationally perturbed, leading to changes in the previously established orbit, and these need to be monitored.

The astrometry of asteroids is similar to comet astrometry, with the exception that asteroids are somewhat easier to measure, appearing as singular dots of light without the complexity that accompanies the expansive head of a comet.

It is recommended that serious astrometric measurements follow the guidelines set out by the International Astronomical Union's Minor Planet Center (MPC), available online at www.minorplanetcenter.net/iau/info/Astrometry.html.

The basic workflow for the astrometric measurement of an asteroid is quite straightforward. First you need to obtain a set of images that include the object you intend to measure. Then you'll need some software assistance to measure the position accurately; the shareware Astrometrica is highly recommended.

Astrometrica allows you to 'blink' your images, which should reveal the asteroid moving against the static star field. The software will need to identify the star field in the images in order to determine the asteroid's position. You can help here by manually identifying the star field and supplying Astrometrica with the correct RA and dec. coordinates for the center of the imaging frame. Once entered, the program attempts to match the star field.

If it doesn't quite get things right, you can adjust the alignment manually. Astrometrica's star template can be adjusted for scale with a focal length used setting, for rotation with a position angle setting and positionally with an onscreen arrow key pad. Once the alignment has been set, clicking on the object will generate an MPC compatible log file of positional data which can then be submitted according to the submission guidelines.

Project 3: Asteroid photometry

Accurately plotting of the brightness and shape of distant asteroids is a team effort

Occasionally an asteroid will pass in front of a star, dimming the star's light as it goes. There are numerous programs available to predict such events as well as websites, such as Euraster, which presents results without you having to having to calculate them yourself.

A typical asteroid occultation path will be a narrow track and may require you to travel to a specific location in order to view and record the event. This adds additional complexity in that it requires the use of a portable observing and recording setup and a means to accurately calculate your location and altitude. The modern way to do this is with some form of GPS recorder.

One of the hardest parts of observing asteroid occultations is to locate the star that is going to be occulted. This can be done using a Go-To system, but you often need to use very accurate star charts to augment the process, especially when the star to be occulted is very faint.

A common way to record asteroid occultations is with a low light video camera. The resulting video, normally recorded in the AVI format, can then be analyzed by specialist programs such as LiMovie or Tangra, which are both available for free.

A successful occultation should produce a light graph for the star that shows it dim as the asteroid passes in front of it and brighten as the asteroid moves out of the way. Accurate timing of the star's dimming will produce a line profile across the asteroid. Interesting though this is, such profiles really become useful when multiple observers record and communicate these events. With multiple profiles recorded, it's then possible to produce a more complete profile of the asteroid.

Obviously for this to be of any worth, a highly accurate time signal needs to be used. A device such as the International Occultation Timing Association's video time inserter (IOTA-VTI; https://occultations.org) is an ideal way to do this as it has the capability to insert coordinated Universal Time (UTC) on every frame of a recorded video signal.

ABOUT THE WRITER
Pete Lawrence is an expert astronomer and astrophotographer who holds a particular interest in digital imaging.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

The Wonder of Satellites

Astro imager Will Gater explores the photo opportunities presented by the myriad spacecraft that can be seen speeding overhead through the night.

AEHF (Advanced Extremely High Frequency) Satellite. Image By USAF (Los Angeles AFB) [Public domain], via Wikimedia Commons

Nightscapes with a bit of Sparkle

Nightscape images that contain glinting Iridium flares or space stations have been a staple of astro-imaging for decades. For beginners, they're great targets to practice your skills on, and it's possible to get really striking images with a basic setup consisting of nothing more than a DSLR and tripod. If you have a bit more experience, don't dismiss shooting a satellite or space station; even advanced photographers can find fresh challenges in experimenting with the framing and foreground of such photos, and in finessing the quality of the final shot. Done well, these pictures can really spark the imagination in ways that other types of astro-images might not.

The timing, brightness and location on the sky of any potential Iridium flares is dependant on your location, so — just as with ISS and other bright-satellite passes — in order to find out when and where one will be visible from your site you'll need to consult a website like Heavens Above (www.heavens-above.com). Once you have this information you can set about planning your shot.

The free planetarium software Stellarium (www.stellarium.org) is particularly useful for this as you can use its plugins to overlay a rectangle showing the size of your camera's field of view on the sky. By cross-referencing the Stellarium view with the information and star chart from Heavens Above, you can identify the path and position of whichever satellite you're aiming to catch and try out different compositions. Stellarium can show the track of the ISS on the sky, and the paid app SkySafari Plus can also perform the same task.

Shooting a series of consecutive 10- to 20- second exposures at a mid-range ISO with a DSLR, kit lens and static tripod will pick up most bright satellite passes. With Iridium flares, aim to start capturing images about 90 seconds prior to the predicted flare time and end the series about the same amount of time after the flare reaches its brightest; this way you'll capture a pleasing trail that slowly builds in brightness, peaks, then fades away. You can then bring the series of images you've captured into processing or stacking software and combine them, so that the short trail in each photo joins the others to form a longer one.

Since most satellites zip across the sky, capturing a series of photos from a static tripod will result in gaps in the final 'combined' satellite trail due to the short delay between exposures. To get around this you can mount your camera on a tracking mount and take one, much longer, single exposure. This requires balancing the exposure length — which will need to be several minutes — with the lens aperture, ISO setting and sky brightness, but can produce attractive unbroken satellite trails against rich, starry skies. Remember, if you do this any foreground will be slightly blurred.

A Split-Second Spectacular

One of the most exciting areas of satellite astrophotography to develop in recent years is imaging the International Space Station passing in front of the Sun or Moon. Imaging these 'transits' requires extensive planning, but the resulting pictures are extraordinary. A typical transit might last seconds, — sometimes much less — and will only be visible from within a narrow strip of Earth's surface. To find out when an ISS transit is visible near your location you can use the excellent ISS Transit Finder (transit-finder.com). If you intend to image a solar transit, where the space station is silhouetted against the disc of the Sun, you'll need to use a certified solar filter for your telescope and be sureto remove any finderscopes. Here are the key steps required to capture this thrilling phenomenon with a scope and DSLR camera.

Step 1: Plan
Find out when a transit will be visible nearby using the ISS Transit Finder website. You may have to travel to be in a position to capture the event. Use planetarium software to check where in the sky the Sun or Moon will be.

Step 2: Setup
Next set up your scope and have it track at the solar or lunar rate (depending on your target). If you're imaging the ISS transiting the Sun, fit a specialist, certified solar filter and remove any finder scopes.

Step 3: Focus and exposure
Focus the view — use the terminator if viewing the Moon, or sunspot or the solar limb if viewing the Sun. Whether you capture stills or video, make sure that the exposure length is very short so that the ISS does not blur.

Step 4: Capture video or a rapid burst of stills
Start capturing video or a burst of stills as the moment of the transit approaches; that way if there is a slight error in your timing you'll still get the shot. For a DSLR video use the highest frame rate that the camera allows.

Step 5: Review, extract and process
Review and process the frames from our video or still images that show the ISS. Software such as PIPP (https://sites.google.com/site/astropipp) can extract still frames from videos. Then process and enhance the images.

Catch a Dragon

If, like us, you remember fondly the days of NASA's Space Shuttle, you may well recall that on occasions the spacecraft and its — just-detached — external fuel tank would be visible passing over the UK shortly after launch. There was nothing quite like watching the rocket roar off the pad live on NASA TV then seeing the very same shuttle and orange fuel tank — both appearing as points of light; the orbiter appearing white, the fuel tank a subtle ochre tint — silently glide overhead. Though the Space Shuttle is no longer flying, there's still occasionally a chance to catch a similar spectacle thanks to one of the new generation of ISS-servicing spacecraft: SpaceX's Dragon capsule.

Whether you'll be able to see the capsule on its way to the ISS just after lift off depends on the conditions of its launch. For the capsule to be visible, it needs to be dark or deep twilight in the UK, but the Dragon itself has to be in sunlight as it flies over. Helpfully, the CalSky website (www.calsky.com) publishes visibility predictions for some of the Dragon spacecraft around the time of scheduled launches to the ISS; you simply input your location details and it will tell you if the Dragon will make any visible passes. The pass you want to look out for — if it's listed — is the one that's about 20 minutes after the expected launch time, as that'll be the Dragon making its first flyover after departing the Florida coast. It's worth keeping an eye on either the NASA TV or SpaceX online video stream that usually accompanies the launch too, as it'll let you know if the lift off gets scrubbed.

One of the things that's so exciting about catching the ISS-bound Dragon just after lift off is that, from here in the UK, it's not just the capsule you get to see. Dragon is propelled into orbit by a SpaceX Falcon 9 rocket, and the separated upper stage of that rocket is visible next to the capsule as it passes over.

Not only that, but Dragon itself jettisons two solar-panel covers after lift-off and these appear either side of the spacecraft as two points of light which repeatedly brighten and fade during the pass as they tumble away. It's a truly electrifying sight and one that can be captured easily using a DSLR, static tripod and 50-100mm lens, and the same basic technique described in 'Nightscapes with a sparkle'. We've even been able to film Dragon firing one of its thrusters during a pass, using a DSLR and a telephoto lens.

The ISS up Close

Ordinarily, high frame rate cameras are used to create detailed images of targets like the lunar surface and planets. But it's also possible to use them to capture high-resolution shots of the ISS showing its modules and solar arrays.

The primary challenge with this type of imaging is tracking the rapidly-moving ISS, since most high frame rate camera and telescope combinations will provide a small field of view that is tricky to keep centred on the station.

Tracking is typically done manually with the help of an accurately aligned finderscope and the mount's handset set at the highest possible slew rate or, in some cases, carefully manoeuvring the telescope by hand. Essentially you start your computer recording a video from the camera and hope that at some point during the pass your guidance causes the ISS to race through the frame.

Focusing can be done in advance on a bright star — or even better, the Moon — while the correct exposure length will depend on the setup you're using; crucially it'll need to be short enough to stop the ISS from blurring and this may mean that you have to greatly increase the camera's gain to compensate.

Fade to Orange

The reason it's possible to see the ISS against the starry sky is that, at the altitude of its orbit, it's still illuminated by the Sun. Sometimes, however, the ISS will disappear into the darkness of Earth's shadow. Just before it does that you can see and image one of the most beautiful satellite phenomena of all: the ISS experiencing 'orbital sunset'.

As the station slips into the shadow, the Sun sinks below the Earth's limb as seen from the ISS in orbit. In the last moments leading up to that 'sunset' the whole structure is bathed in a deep-orange light. And because that light is the same sunlight that illuminates the station as it passes over us, from the ground the ISS turns from a brilliant white to a deep orange-red, before disappearing.

This effect can be seen clearly in binoculars from suburban sites, but is a particularly rewarding target for imagers and naked-eye observers under darker skies. The passes in which the ISS moves into Earth's shadow are clear in the night-sky charts that accompany each ISS pass prediction on Heavens Above (www.heavens-above.com); they're the ones where the pass seems to abruptly 'stop' amongst the stars. Point your camera in the direction of that end point and — with a long exposure of a minute or so using a DSLR on a tracking mount — you should pick up the gradual fade to orange in the ISS's trail.

What is an Iridium flare?

Iridium 'flares' appear as a brief and slow-moving point of light that brightens rapidly and fades just as fast. They are produced when the antennas of any of the numerous of Iridium communications satellites catch the Sun's light and reflect it back to Earth. In January, the first in a new fleet of Iridium satellites was launched. The antennas of these new satellites aren't as reflective, so the days of Iridium flares could be numbered.

ABOUT THE WRITER
Will Gater is an astronomy journalist, author and presenter. Follow him on Twitter at @willgater or visit willgater.com

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

The Sky in Motion

Astronomer Will Gater reveals the best way to observe and image transient and evolving celestial phenomena, and how you can help scientists in the process.

This NASA Hubble Space Telescope set of images from Sept. 10, 2013 reveals a never-before-seen set of six comet-like tails radiating from a body in the asteroid belt designated P/2013 P5. Image Credit: NASA, ESA, D.Jewitt/UCLA

For most of us our interest in astronomy is, and hopefully will continue to be, a lifelong passion. In 10, 20, even 30 years from now we'll look up to the night sky and in the stars, galaxies and nebulae that fill our view we'll see old friends, unchanged over all that time. The truth is, of course, that the stars and galaxies we see are moving through space, and nebulae are evolving — they're just changes that are unfolding on an extraordinarily long cosmic timescale.

But that's not to say that we humans can't perceive any alteration or movement in the night sky. Quite the opposite. One could argue that the heart of amateur astronomy — and indeed one of the key elements of astronomy as a field of scientific study — is a rich and deep tradition of observing the changing night sky, from the appearance of comets to the monitoring of variable stars and the searches for supernovae in distant galaxies.

In the following pages we're going to explore some other transient and evolving celestial phenomena that you can observe and photograph with relatively simple equipment — the kind of kit that many amateurs have access to — so that you can see for yourself that the sky, and indeed the cosmos all around us, really is in motion.

Watch an Asteroid Whizz By

While the planets might be the quintessential 'wandering stars', drifting against the night sky's sparkling backdrop over weeks and months, there are other objects within the Solar System whose movement across the heavens is far more dramatic — so much so that their motion against the stars can be discerned over hours and minutes, rather than many days. Near-Earth asteroids are small, typically irregularly shaped bodies, whose orbits bring them relatively close to our planet at times. If a near-Earth asteroid is big and bright enough it can be a thrilling object to catch sight of in a telescope eyepiece, or capture on camera, as it makes a close approach. ESA maintains a database at http://neo.ssa.esa.int/web/guest/close-approaches that you can examine to see when any large, relatively, bright objects are next passing by — and of course the BBC Sky at Night magazine Sky Guide will usually contain news of upcoming notable near-Earth asteroid passes.

Capturing a Near-Earth Asteroid Pass on Camera

Watching a near-Earth asteroid slowly wander across a star field at the eyepiece can be tremendously exciting, but it's the sort of target that really requires a medium- to large-aperture instrument to be seen well. On the other hand, even a modest astrophotography setup can capture brighter near-Earth asteroids — here we explore how.

Step 1 — Equipment
Small refractors or Newtonians combined with a CCD camera or DSLR are well-suited to imaging bright near-Earth asteroids; we've even had success using just a DSLR and a 135mm telephoto lens. You'll also need a mount that can track the sky accurately for a few minutes at least.

Step 2 — Track and focus
Set up your imaging kit. If you're using an equatorial mount get the polar alignment (and thus the mount's tracking) as accurate as you can, as this will help both image quality and processing later on. Next, focus on a bright star — ideally with the help of a Bahtinov mask.

Step 3 — Locate and image capture
Use Stellarium (stellarium.org) and its Solar System Editor plug-in to find a near-Earth asteroid's location. Slew to the coordinates, take brief test exposures, then cross-reference the star field with Stellarium. When you've confirmed the near-Earth asteroid is in frame, check it's not moving out of shot. Capture a series of exposures.

Step 4 — Stack or animate
You should now have a set of images (typically taken over several tens of minutes) that shows the near-Earth asteroid moving between frames. You can now process and stack these together with your chosen image processing software to show the asteroid's path, or collect and save the frames as an animated GIF.

Marvel at a Lunar Sunrise

As astronomers we're familiar with the Moon's phases, caused by its movement around the Earth and the changes in illumination that come from the varying geometry of the Earth, Moon and Sun relative to one another. Prior to full Moon, the boundary demarcating night and day on the lunar globe, and the line that gives the phase its 'shape' — called the terminator — is the swathe of terrain where the Sun is rising over the lunar landscape. At this point in the lunar cycle the phase is waxing (growing), as the terminator travels across the disc. After full Moon the terminator moves westwards from the eastern limb once again, but is now where the Sun is setting, with the phase waning (shrinking).

This night-by-night movement of the terminator, and consequently the daily change in the lunar phase, is large and easily visible to the naked eye. But you can also observe and image subtle variations in the Moon's phase over the course of just one night. Watching the Sun rise or set over a chain of mountains or a large crater rim is a captivating observing experience; it is quite something to see the lighting change, and shadows lengthen or shorten. It's evidence of the Moon's orbital motion, happening right in front of your eyes.

The UK winter months, when the Moon is high for hours in a dark sky, are an ideal time to attempt the observation. Our favourite targets to see this phenomenon on are the large craters Copernicus and Plato — the latter especially, for the shadows from its rim that creep across its smooth floor — the lunar Alps and the Sinus Iridum.

A high frame rate camera and a modest amateur telescope can capture the changes easily. If you are able record an AVI video every 20-30 minutes or so for several hours, you can create dramatic animations of the changing illumination. This requires each processed image produced from the raw AVI videos to be brought into software — such as Photoshop or GIMP — as a separate layer. Multiple layers within a single picture can then be saved as an animated GIF file.

How You Can Help The Professionals

Taking pictures or making observations of some of the phenomena we've covered in this article can be an exciting experience in itself, but it's also possible that your records could help professional astronomers with their research. For example, if asteroid imaging is your thing, the scientists working on the OSIRIS-REx mission — which will return samples from the surface of the asteroid 101955 Bennu in 2023 — run a project called Target Asteroids! (https://www.asteroidmission.org/get-involved/target-asteroids) It uses data captured by amateurs to help learn more about certain asteroids. Alternatively, if you've been lucky enough to capture a picture or timelapse of the Northern Lights on holiday, the Aurorasaurus citizen-science project (http://aurorasaurus.org) is collecting images of a poorly-understood auroral phenomenon dubbed, rather unusually, 'Steve' — if your snaps show the unusual filamentary feature they could be useful to researchers.

And of course many national astronomical societies and organisations gather reports and observations of transient and changing astronomical phenomenon sometimes for publication and analysis in their journals.

So whether it's through a citizen-science project or a more traditional endeavour, like meteor counting, planetary imaging or variable star observing, there are many ways that we amateurs can make a meaningful contribution.

The Spectacular Seething Sun

We needn't look lightyears out into space to find evidence of the dynamic and ever-changing nature of the cosmos we live in. In fact you'll find it on our celestial doorstep in the form of our star, the Sun. This seething ball of plasma is constantly changing. Its churning 'surface' — the photosphere — is occasionally pockmarked by dark, transitory, blemishes known as sunspots, while above huge tendrils of plasma, called prominences, rise and waver as they are corralled by the star's magnetic fields.

To observe these features safely however you'll need specialist equipment. To study the photosphere, for example, a telescope needs to be fitted with a certified solar filter and any finder scopes should be removed too. With careful and correct use and installation — conforming to the manufacturer's instructions — certified solar filters can provide superb views of evolving sunspots and large sunspot groups.

There are also specialist dedicated solar telescopes available which, as well as filtering the Sun's light so it is safe to view, show only certain specific wavelengths of the Sun's radiation. One type of dedicated solar telescopes shows what's known as the 'hydrogen-alpha' band in the Sun's spectrum. These solar scopes reveal a layer in the Sun's atmosphere known as the chromosphere and in doing so open a window onto one of the most dynamic regions of our star.

While an ordinary certified solar filter will show the solar photosphere as a smooth whitish or yellowish disc, perhaps marked by sunspots or speckled bright patches known as faculae, a hydrogen-alpha solar telescope will show the Sun's chromosphere as a bright, scarlet-red globe shrouded in a mass of plasma 'fibres'.

A hydrogen-alpha solar telescope will also often reveal the prominences leaping off the limb of the Sun, and these can change in literally a matter of minutes, meaning they are a wonderful target for high-resolution imaging where spectacular animations can be made of their evolution. Sketching can be a great way to record the changes in these features too.

The powerful magnetic fields associated with sunspots also have an effect in the chromosphere. There they manifest themselves as bright 'active regions' where loops of plasma twist and turn around the dark sunspots. Like prominences these too can change and evolve over short periods. Sometimes they may even exhibit very bright, fleeting, beads or filaments of light. These are thrilling events for solar observers and imagers, and are known as solar flares.

Create a Timelapse of the Turning Sky

One of the most obvious signs that we live on a rock spinning in space is the motion of the stars across the sky during the course of a night. This movement is a result of Earth rotating on its axis, and you don't need a hugely advanced setup to capture it on camera; a DSLR, wide kit lens and static tripod are ideal for tackling a classic star trail shot. Leave the shutter open for 30-60 seconds and the rotation of the Earth will blur the stars into short arcs. If you want to take things a step further, try creating a timelapse of the sky — and perhaps the Milky Way too — moving. You can use the same kit as for a star trail shot, but you'll need to approach the way you capture the images in a slightly different way. For timelapses you don't actually want the stars to trail. What you need are for them to be points of light so that when you come to animate the shots it looks almost as if the sky is a static picture that's drifting over a landscape. This may mean that you have to keep the exposure length short, increase the ISO and open your lens's aperture right up to compensate. When you've found the right settings, set the camera taking exposures continuously, say for 30 minutes for a short timelapse. You'll typically capture hundreds of photos doing this, so make sure your camera's memory card and your computer are up to the task! The images can then be processed as a group in image processing software and then imported into a video editor to be animated into a smooth video. There are numerous ways of achieving the latter — for example in iMovie you'd do it by setting the 'duration' of each still image to 0.1 seconds. This technique can also be used to make timelapses of other dynamic astronomical phenomena, such as aurorae and noctilucent clouds.

The Skies In Motion This Month

A particularly fine chance to watch the motion of the heavens is on offer in the UK this month when, in the early hours of the morning on 6 November, the gibbous Moon will occult (slip in front of) the bright star Aldebaran in Taurus. As the Moon journeys across the background stars of Taurus, Aldebaran will disappear behind the brightly lit western limb of the Moon, emerging 40-60 minutes later from behind the unlit eastern limb. Occultations are great events for video astronomy, so if you have a digital camera that can shoot video try capturing Aldebaran suddenly popping into view as it reappears from behind the Moon. The exact moment of Aldebaran's reappearance (and disappearance) will depend on where in the UK you're observing from, so consult a planetarium programme, such as Stellarium (http://www.stellarium.org), for location-specific times.

ABOUT THE WRITER
Will Gater is an astronomy journalist, author and presenter. Follow him on Twitter at @willgater or visit willgater.com

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Chasing the Moon's Shadows

This summer, Elizabeth Pearson travelled across the US to hunt down the total eclipse of the Sun on 21 August 2017.

By Zombiepedia - Own work, CC BY-SA 4.0, Link

In 1999, a total eclipse of the Sun passed over Cornwall. And I missed it. Ever since, I have wanted to see totality, and so when I heard that the Moon's shadow would be passing coast to coast over the US mainland on August 21st 2017, I knew I had to be there. I decided to take a road trip that would end up taking me almost 3,000km across the country as I attempted to chase down the lunar shadow.

My journey started in Salt Lake City, Utah, where I picked up the hire car that would prove to be my faithful steed for the week. My first stop was Salt Lake City's Clark Planetarium, where I found queues out the door. The crowds had been brought in by an email from a major online retailer recalling eclipse glasses, sparking a panic.

"A lot of people who thought they had glasses just got emails saying their glasses cannot be trusted, and have come to the Clark Planetarium because we have the real ones. We never thought we'd be the only supplier in town. We have a supply for today, we may even have a supply for tomorrow, but then who knows," says Seth Jarvis, the director of the Clark Planetarium.

Like most of the nation, Salt Lake City would only see a partial eclipse, making appropriate eyewear crucial. But for me, the 91 per cent it would see wasn't enough. I wanted totality. It was time to start chasing that shadow.

As I drove from Utah into Wyoming, I began to see signs that I was heading into totality country. On the highways there were notices banning heavy vehicles on August 20-22 to keep traffic moving, while in towns handwritten signs offered eclipse parking. Every business, it seemed, had special 'Totality Deals'.

The Building Buzz

Eventually I made it to Casper, Wyoming, the largest town on the eclipse's central line and host to the Astronomical League's annual AstroCon convention — which happened to coincide with my visit. The event had drawn people from all over the world, keen to see the eclipse.

"Once you've seen totality, you've just got to see it again," says Sue Baldwin, an eclipse chaser from Auckland, New Zealand. "The first time I saw it I bawled my eyes out for 30 seconds, and actually had to hit myself so I could look at the totality. It's just that emotional, there is no comparison."

With so many eclipse enthusiasts together under one roof I couldn't help picking up on their excitement. And it only grew when I drove on to my next pit stop of Alliance, Nebraska. "They're saying that there are going to be 20,000 people in town altogether," says Jessica Hare, the acting manager for local monument 'Carhenge', a replica of Stonehenge made from scrap cars and the reason this remote location is so busy when I arrive.

"For the most part people in town are excited. There's a reason we live here, though: we're not into big crowds," Hare continues. "But it's a change of pace for a few days and then we've got something to talk about for 60 years."

With only two days to go, people were already arriving and setting up camp. But amongst the bustle, an air of disquiet was beginning to form. People were checking the weather and all was not well. On August 21st, clouds were forecast across the eastern side of the US. Combined with the eclipse glasses scare, it looked like huge numbers of people might not get to witness the great event.

By the time I reached Sutherland in central Nebraska, where I had planned on watching the eclipse, the forecast had grown even worse. The nearest place with completely clear skies forecast was almost 400km back the way I had just come, along roads already gridlocked with traffic. Did I stay and risk being clouded out, or go and risk getting stuck on the highway?

I had come too far to end up staring at clouds. Time to chase those clear skies. Wanting to avoid the most horrific traffic, I picked a town just off the centerline and at 4am on 21 August, I was back in the car.

As I set off, the fog was so thick that at times I could barely see 30m ahead of me. But I was determined to beat the clouds and fought on until four hours later I reached my final destination — an old airfield in Mitchell, Nebraska. A few hundred people had already arrived, most of whom had also undertaken long treks, and were ready to see their first eclipse when it started at 10:25am.

The Moment of Darkness

When the hour came, we donned our (certified) eclipse glasses to watch as the Sun was slowly eroded away by the Moon. As the spectacle unfolded, the dwindling sunlight made its effect felt. The air, which should have been uncomfortably hot by now, felt more like a breezy afternoon.

With around 20 minutes to go, I reached to take my sunglasses off before realising I wasn't wearing them. The light was fading and taking the colour out of the world with it, like an old photograph that's been left in the Sun.

At 11:46am, with one minute left, the Sun was down to the merest sliver. I turned to the west to watch as a wall of darkness seemed to advance across the sky.

Turning back, I watched as a sudden explosion of diamond light came from the Sun as the last of its rays were covered, accompanied by a huge cheer from the crowd.

Where once the Sun had been, there was now a hole of utter blackness. A crown of light danced around it and I could almost see the fine tendrils swaying with the breeze. It seemed huge, stretching over a much larger area of sky than I'd expected. Around me, the sky was in twilight with pink trimming every horizon, as if the Sun had just set in all directions together.

The crowd was quiet now. After all the excitement and panic, I felt a sense of quiet calm. I was under the shadow of the Moon, watching plasma arcing a million kilometres out of the Sun. It was humbling, a reminder of our small place in the grand Universe.

The Chance of a Lifetime

All too soon, I could tell totality was reaching its end. The perfect circle of blackness was beginning to look lopsided. One minute, 53 seconds after the first, there was a second burst of light as the shadow passed, sweeping across the nation and taking the spectacle to the millions who waited farther east. As others rushed home, I stayed to watch as the Sun returned, taking a moment to appreciate what I had just witnessed.

Later that evening, back in Sutherland (where the weather had been perfect, of course), I headed out to look at the Milky Way, knowing our Galaxy is only one of billions that all move together in the ballet of the Universe. I've devoted my life to studying that dance, but I have never grasped its majesty like I did in that one minute and 53 seconds.

Once you've seen totality, you really do have to see it again. On April 8th, 2024, another eclipse will sweep across the US and I plan on being under the Moon's shadow once more. Maybe I'll see you there.

Stargazing Central

Sandhills, NE
The rural state of Nebraska is home to some of the darkest accessible skies in the world, making it a dream destination for deep-sky imagers.
https://visitnebraska.com/stories/visit-the-sandhills

Strategic Air and Space Museum, Omaha, NE
The museum is home to several space artefacts and a tribute to Nebraskan astronaut Clay C Anderson, as well as dozens of aircraft.
http://sacmuseum.org

Clark Planetarium, Salt Lake City, UT
As well as shows in the dome, the Clark Planetarium houses a space museum with interactive exhibits to enthuse little astronomers.
https://slco.org/clark-planetarium

Yellowstone National Park, WY
Spend the days exploring the world-class park and the nights taking in the dark skies. An astronomy program runs in summer.
www.nps.gov/yell/index.htm

Carhenge, Alliance, NE
This huge replica of Stonehenge made from cars was built in 1987 as a tribute to the artist's father, and has proved to be a popular road trip stop ever since.
http://carhenge.com

Craters of the Moon, ID
Follow in the footsteps of the Apollo 14 crew, who underwent geology training in this volcanic landscape prior to their trip to the Moon.
www.nps.gov/crmo/index.htm

ABOUT THE WRITER
Dr Elizabeth Pearson is BBC Sky at Night Magazine's news editor. She gained her PhD in extragalactic astronomy at Cardiff University.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Why We've Got to Get to Mars

He may be one of the most famous moonwalkers, but Buzz Aldrin has spent the past 30 years developing a plan to get people to Mars. He tells Jamie Carter why.

By ESA - European Space Agency & Max-Planck Institute for Solar System Research for OSIRIS Team ESA/MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA - http://www.esa.int/spaceinimages/Images/2007/02/True-colour_image_of_Mars_seen_by_OSIRIS, CC BY-SA 3.0-igo, Link

Colonising the Solar System is becoming the 'in' thing among billionaires. SpaceX supremo Elon Musk recently talked putting a million people on the Red Planet within 100 years, while Blue Origin's Jeff Bezos thinks he can help spread a trillion people throughout the Solar System. That's big talk, but there's one man who's spent the last three decades telling anyone who'll listen about his plans to go to Mars, and why it's so important we do so.

"I'm 87 years old and I'm getting impatient," says Dr Buzz Aldrin, who walked on the Moon in 1969 as part of Apollo 11. "We've been stuck in low-Earth orbit for too long and I believe that we need to break this malaise," he says. "I do believe we can establish permanent habitation on Mars by 2039, and I have a plan to achieve it."

If that date seems rather specific, there's a good reason for it: it would be the 70th anniversary of Apollo 11's Moon landing. Not that Aldrin wants to be constantly reminded of that. It may be regarded as a seminal moment for humanity, but only until someone sets foot on Mars. "I want to be remembered as the man who led the world to Mars, for a permanent settlement," he points out.

Occupation vs. Exploration

Aldrin, who is constantly refining the ideas he first set out in his 2013 book Mission to Mars: My Vision for Space Exploration, now wants to play a pivotal role in the push to the Red Planet. But there remains a fundamental question: why do we need to occupy Mars? Why not just pay it a quick visit?

"What concerns me most about expeditionary missions is that we may go there once or twice and never go back — it would be flags and footprints again," says Aldrin, citing the Apollo Moon landings, the last of which was 45 years ago. "But the more important reason is that it's vastly more expensive to send people up there with all their infrastructure in one spacecraft and the quality of the science would be dramatically lower."

According to Aldrin, once you have the right kind of surface and transportation infrastructure, the cost of sending individual astronauts would be affordable. His is a pragmatic plan built upon orbital calculations that could make inhabiting Mars far more affordable than anyone imagines.

Aldrin's idea revolves around the concept of 'Cycling Pathways': one or possibly two Earth-Mars spacecraft (a 'Cycler') that travel constantly between Earth and Mars. "The astronauts will be transported to the Earth-Mars Cycler with a single launch, with refuelling in Earth orbit," explains Aldrin. "Using spacecraft that cycle between Earth and Mars would be an order of magnitude cheaper than using an entirely new series of rockets to send each crew to Mars."

Following on From Von Braun

Although his ideas pre-date those currently being proposed by various billionaires, Aldrin is certainly not the first to consider how to carry out a manned mission to Mars. Dr. Wernher von Braun, developer of the Saturn V rocket, briefed NASA's Space Task Group just after the Moon landings on a plan to land two expedition spacecraft on Mars in 1982. "Werner von Braun's vision of Mars exploration was a tremendous inspiration to many of us," says Aldrin. "But von Braun was really interested in using very large rockets. I think we can get to Mars without the same reliance on state-developed and operated rockets." Aldrin's plan also differs from Von Braun's in its level of reusability.

Ambitious space exploration plans always come with a huge caveat: politics. Aldrin was recently at the White House, standing alongside President Donald Trump as he signed an executive order re-establishing the National Space Council after its 24-year hiatus, but he's not getting too carried away with that decision. "I don't expect the Space Council to fundamentally change the US space programme by itself. But it will really become critical if the administration decides to fundamentally rethink major aspects of our civil and national space programmes," says Aldrin. That's what he's hoping for.

Aldrin will be keeping a close watch on what President Trump says on 24 July 2019 when the world marks 50 years since Aldrin and Neil Armstrong set foot on the Moon. "I'm personally very committed to the idea that the President should, and indeed must, announce a major US commitment to Mars permanence by the 50th anniversary", he says. "It's essential to force us to make the hard choices we must make in order to get to Mars in the next 20 years."

ABOUT THE WRITER
Jamie Carter is the author of A Stargazing Program for Beginners: A Pocket Field Guide and edits WhenIsTheNextEclipse.com

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Secrets Erupt from Jupiter

In January 1979, after a journey of 15 months, Voyager 1 began to photograph the first planet on its Grand Tour, the gas giant Jupiter. Voyager 2 followed a few months later, and together they rewrote almost everything we thought we knew about the Jovian system — not least the fact that volcanism exists beyond Earth.

Photograph by Cherdphong Visarathanonth in Prawet district, Bangkok, Thailand

At first glance, it resembled nothing more than a blemish on Voyager 1's lens. But as 26-year-old engineer Linda Morabito peered closer at the image of Jupiter's moon, Io, she realised she was looking at something extraordinary. The blemish was actually a faint, bluish crescent that was protruding from beyond the moon's limb.

This all occurred on 9 March 1979, four days after the probe had made its closest pass — 349,000km — of the broiling Jovian cloud tops. Morabito was part of the optical navigation team, plotting Voyager 1's trajectory to Saturn, three-quarters of a billion kilometres and 20 months away. She had just made the most significant discovery of the entire mission.

The long-exposure shot, taken a day earlier, viewed Io from a parting distance of 4.5 million km. Analysis revealed the crescent to be a plume — rising over 280km into space — from a volcano. Later named 'Pele' after the Hawaiian goddess of volcanoes, it was the first of hundreds of such features to be found on Io. As the days wore on, infrared data pinpointed regions rich in sulphur dioxide, where temperatures soared up to 200°C higher than the surrounding terrain. Four months later, on 9 July, Voyager 2 revealed that Pele had fallen dormant, although several other volcanoes remained active.

Big Surprises

It was a big surprise on a natural satellite with a size and density roughly equal to that of our geologically inactive Moon. Io's proximity to its giant host (it orbits just 421,800km from Jupiter's centre) forces it to bear the brunt of a punishing magnetic field. This is hundreds of times stronger than Earth's and 'co-rotates' with Jupiter's interior every 10 hours, transporting vast quantities of energetic plasma back and forth along magnetic field lines. The field is inflated at the magnetic equator, pushing the plasma outwards in a huge, tilted 'sheet' that rises and falls, flopping north then south, during each rotation period.

The relationship between Jupiter and Io is a complex one. As Jupiter's magnetic field sweeps past Io it strips 1,000kg of mass from the moon every second. This forms a doughnut-shaped 'torus' of charged particles, the existence and extent of which was first inferred by Pioneer 10. Ground-based observations also identified a neutral sodium cloud around Io, formed by atmospheric sputtering, as well as the spectroscopic fingerprints of sulphur dioxide.

Not until the discovery of Io's volcanism did the process of how this torus was maintained begin to make sense. Under Voyager 1's gaze, twice-ionised oxygen and sodium atoms glowed brightly at ultraviolet wavelengths. To achieve such intensities, electron temperatures have to surpass 100,000°C and radiate a trillion Watts — double the power-generating potential of the entire US — along a 'flux-tube' into Jupiter's magnetosphere. Voyager 1 tried to fly through this flux-tube, but missed its centre by around 5,000km.

Lava Lakes and Lights

Morabito's chance discovery identified Io as the most volcanically active place in the Solar System. It yields twice as much energy as all of Earth's volcanoes combined, despite having a fifth as many hotspots and being only a third of the size of our planet.

Voyager 1 found virtually no impact craters on its young and dynamic surface, just a few per cent of which was pockmarked with dark-centred volcanoes. From these snaked red and orange lava flows, some fanning out in wide arcs, others forming a series of twisting tentacles. Pele was surrounded by a hoofprint-shaped lake of sulphur dioxide, while 200km-wide Loki — more powerful than all of Earth's volcanoes, put together — had increased in magnitude and evolved into a two-plume eruption by the time Voyager 2 was able to observe it.

Jupiter's torus offered a contributing reservoir of energetic particles, which spiralled along magnetic-field lines to fuel the planet's spectacular aurorae. One display extended 30,000km across its north polar region and generated extraordinary 'whistling' radio emissions. The Voyager 1 image that confirmed the existence of the 'Jovian Lights' also picked out massive electrical discharges from 19 lightning 'superbolts', while Voyager 2 went on to locate eight additional flashes.

Jupiter's magnetosphere is a truly colossal powerhouse. The Pioneer probes revealed its sunward extent and raised speculation of a bullet-like 'magnetotail' in its wake. Voyager data confirmed the tail's existence and showed that it extended 740 million km beyond the planet, as far as Saturn's orbit. Increased solar activity since 1974 had compressed the sunward boundary and a continuous push-pull dynamic saw both spacecraft repeatedly enter, exit, then re-enter the magnetosphere — Voyager 2 recorded 11 boundary crossings. This showed the variability of the magnetosphere's size, as the boundary rhythmically flashed in and out in response to solar wind pressure.

Moving Pictures

The two Voyagers spent months examining Jupiter, both before and after their closest passes. From January until April 1979, Voyager 1 transmitted data across the 778-million-km gulf to Earth, while Voyager 2 did likewise between April and August. Pictures received during those periods showing how the differential rotation of Jupiter's atmosphere produces a colorful latitudinal display of bright 'belts' and dark 'bands', prompted comparisons to the work of Vincent van Gogh.

Movies made with overlapping photos of Jupiter's rotation showed clouds swirling around the edge of the planet's famous Great Red Spot and clipping along at 100m/s. Twice the size of Earth and observed telescopically since the 17th century, the spot inhabits the southern hemisphere and rotates anticyclonically, bearing many hallmarks of a high-pressure region. With no solid surface or continents to anchor pressure waves, Jupiter's storms can (and do) endure for centuries. The Pioneer probes saw uniform color within the spot and its attendant clouds, but by 1979 south temperate latitudes had altered considerably, producing complex turbulence. In July, Voyager 2 hurtled past at a distance of 576,000km and revealed a notable 'thinning' of bands at the spot's southern rim, a spreading-out of clouds to the east and a greater evenness of color. Three oval-shaped white spots, first seen four decades earlier and each the size of our Moon, had also worked their way steadily eastwards.

A Ring Is Revealed

At 1,300 times the size of Earth, Jupiter is the biggest and most massive planet in the Solar System. Infrared data from Voyager pegged its composition at 87 per cent hydrogen and 11 per cent helium, with trace amounts of methane, water, ammonia and rock. A seething mass of clouds, storms and eddies within its bands and belts moved crisply across its disc, indicating that the motion of material, rather than energy, was at work deep in the interior. Westward-blowing zonal winds extended at least 60° north and south, far closer to the poles than expected. But the surprises didn't end there.

Before 1979, only Saturn and Uranus were known to have rings; theoretical models of long-term stability had not predicted any to exist at Jupiter. That prediction was proven wrong just 17 hours after Voyager 1 made its closest approach, when a photo taken to search for new moons picked out a tenuous ring only 30km wide.

It was intrinsically dark and composed of tiny, rocky grains, with a reddish hue similar to the surfaces of the newly found moons Thebe, Metis and Adrastea. Long-range imagery also revealed a red surface on the elongated and cratered moon Amalthea. This prompted speculation that the ring might have evolved from an ancient moon torn apart by tidal forces and it was argued that Adrastea could provide a suitable reservoir of material for it.

Voyager 2 revealed the ring to be quite narrow — one scientist called it "ribbon-like" — and its proximity to Jupiter implied that it was quite young. Its main body was joined by an interior 'halo' of dust and an outer 'gossamer' ring, which petered out into the background darkness, 180,000km above the planet's cloud tops.

New View, New Details

The Voyager probes unveiled the Jovian system in its entirety for the first time and showed us the vast differences between the four Galilean moons. Even the finest telescopes of the era were only capable of showing Io, Ganymede, Europa and Callisto as tiny, dancing points of light. The two Voyager spacecraft revealed them to be four distinct worlds that varied in size from smaller than our Moon to almost as big as Mars.

Giant Ganymede is the largest planetary satellite in the Solar System, with an equatorial diameter of 5,270km, slightly pipping Saturn's moon Titan. Voyager 1 uncovered the presence of a thin atmosphere on Ganymede with a pressure equivalent to just one billionth of the sea-level pressure on Earth. Images taken by the probe showed a terrain split between dark, heavily cratered ancient areas and brighter, more youthful patches intersected by ridges and furrows.

The dominant feature on Ganymede's surface is the Galileo Regio, a 4,000km-wide dark patch big enough to cover the 48 adjoining US states. This vast oval-shaped remnant of Ganymede's primordial crust is punctuated by craters nicknamed 'palimpsests', after pieces of reused medieval parchment that allow the original, partly erased work to show through the new writing. The region and its craters offer a tantalising glimpse of Ganymede's past tectonic upheavals. Elsewhere, younger craters exhibit dark rays, extending for hundreds of kilometres across the surface.

An Old Moon

Callisto, although eight per cent smaller in equatorial diameter than Ganymede, was expected to be similar, as both moons are approximately half-water and half-rock and, unlike Io, are far enough from Jupiter to escape serious magnetospheric bombardment. Voyager 1 saw Callisto on the outward leg of its journey and found a surface without high mountains or deep ravines but dominated by the 600km-wide bullseye of the Valhalla impact crater and its surrounding array of concentric rings.

Vast tracts of heavily pitted terrain revealed a world whose origin may stretch as far back as the accretional stages of the giant planets themselves, some 4.5 billion years ago. 'Large' craters, exceeding 150km in diameter, were conspicuously absent, however, leading to theories that Callisto's ice-rock composition had somehow altered the ability of its thin crust to support them. Even at the time of the Voyager encounters, it was argued that ice floes over millions of years probably filled and obliterated craters of this size.

As for Europa, the two spacecraft saw the smallest Galilean moon as a highly reflective globe, reminiscent of a "string-wrapped baseball". It was a description inspired by the moon's striking linear features, from its scalloped ridges to meandering dark stripes that crisscrossed the surface for thousands of kilometres, while mysterious 'triple bands' made up of two parallel ridges, separated by a depressed central gorge. One of the few craters on Europa is 26km-wide Pwyll, which is surrounded by bright rays of ejecta that run for hundreds of kilometres out from its central basin.

Interestingly, the Pwyll impact seemed to have occurred on a particularly thin portion of the crust, for iceberg-shaped chunks of subsurface material protruded from its floor. Dark areas, nicknamed 'maculae', were identified as potential upwellings from deep within Europa's interior, while the side of the moon, which faces away from Jupiter was characterised by huge, wedge-shaped bands, many kilometres long.

More to Discover

The Voyagers' discoveries at Jupiter underlined the unpredictability of planetary exploration, for the largest planet in the Solar System had begrudgingly surrendered only a handful of the mysteries it held. For the Voyager scientists, it had been a once-in-a-lifetime experience. NASA's associate administrator for space science Thomas Mutch likened it to "being in the crow's nest of a ship during landfall and passage through an archipelago of strange islands". Volcanism on Io, colossal polar aurorae, along with unknown and unseen rings and moons could never have been confidently predicted before we turned our knowledge-gathering capabilities over to the Voyager robots, millions of kilometres from home; robots whose findings rewrote the textbooks on Jupiter for the next quarter of a century.

The Radiation Problem

Before 1970, it was theorised that large quantities of abrasive dust might endanger a spacecraft as it attempted to pass through the asteroid belt between Mars and Jupiter. Several years later, when the Pioneer probes crossed the belt, they showed the dust was no danger. But upon their arrival at Jupiter, a new problem emerged: the Pioneers' circuits had been fried and their optics darkened by the savage Jovian radiation belts. They'd endured 1,000 times the human-lethal dose of high-energy protons and electrons.

As well as building a plasma-wave instrument to analyse this environment, engineers worked to toughen the Voyager probes' electronics ahead of their visits to Jupiter and Saturn. Radiation-resistant materials, including tantalum, were tested to maximise their reliability, before being added into each of the spacecraft. Particularly sensitive areas received additional spot-shielding.

The Voyagers made it through the radiation belt but not wholly unscathed. Voyager 1 experienced a 'timing offset', which caused its on-board clock to slow down. Moreover, its two computers drifted out of synchronisation with each other and the flight data systems. These glitches led to some photographs being taken 40 seconds too early, which induced blurring and the loss of high-resolution images of Io and Ganymede.

Fortunately, Voyager 2 passed Jupiter at a much wider distance than its twin so its problems were correspondingly lessened. Its computer had also been reprogrammed to synchronize automatically, every hour. In this fashion, the complications of image-smear by the high radiation levels were largely avoided.

A Fresh Glimpse Of An Old Great

Measuring 26,000km in its east-west diameter and half as much north-south, the enigmatic Great Red Spot lies 22° south of Jupiter's equator and has been observed telescopically for more than three centuries. Its discovery is usually attributed either to the English scientist Robert Hooke or the Franco-Italian astronomer Giovanni Cassini, both of whom are believed to have seen and recorded it between 1664 and 1665. Writing in the Philosophical Transactions of the Royal Society, Hooke identified the feature's presence "in the largest of the three observed belts of Jupiter" and noted that "its diameter is one-tenth of Jupiter".

The spot was seen intermittently up until 1713, before seemingly vanishing. Heinrich Schwabe saw it again in 1831. Since then, it has changed both in size and color: ranging from an extraordinary brick-red hue to a more mellow ruddy brown and swelling at one stage to 40,000km in diameter. Voyager observations revealed it to be a high-pressure region, significantly colder at the cloud-tops, although the reason for its color remains a mystery.

Due to the lack of solid surfaces on the giant planets, long-lived storms of this type have been identified on Saturn and Neptune, although not in the same league as the Great Red Spot. It's possible that such features draw energy from the sides or below, or perhaps that they accrue their size simply by gobbling other smaller spots and eddies. It seems that thanks to the immense depth of the atmosphere and the absence of continents to dissipate the storm's energy, the Great Red Spot has settled into a semi-stable state.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Titanic Discoveries at Saturn

Long regarded as the 'wow' planet of the Solar System, Saturn proved more magnificent than anyone had imagined. While it was in the neighbourhood, Voyager 1 skimmed past Titan, still the only moon we know of with a thick atmosphere.

Photograph by Cherdphong Visarathanonth in Prawet district, Bangkok, Thailand

On the evening of 6 November 1980, less than a week before reaching Saturn, Voyager 1 fell abruptly, though not unexpectedly, silent. Bruce Murray, then serving as director of the Jet Propulsion Laboratory (JPL) in Pasadena, California, was not alone in having expressed consternation over the hazardous manoeuvre that was about to take place. After all, the tiny spacecraft was three years into an epic mission of exploration that had already rewritten the textbooks on Jupiter. Now, more than 1.4 billion km from Earth, it was having its critical communications link with Earth intentionally severed so the craft could be turned towards Titan.

"Isn't it risky," Murray asked at one of the last pre-Saturn meetings, "to break communications, so close to encounter?" It was indeed a dauntingly bold move, but there was a clear rationale for it. Voyager 1 was following a route known as 'Jupiter-Saturn-Titan' so it could observe, at close quarters, the only natural satellite in the Solar System definitively known to possess a dense atmosphere.

If it was to fly within 3,900km of Titan's soup-like canopy of gases and particulate haze, a trajectory-correcting firing of the spacecraft's thrusters was needed. And to accomplish that, Voyager 1 had to reposition itself a quarter-turn away from its lock on Earth.

The Deep Space Network's tracking station in Goldstone, California, duly transmitted the requisite commands up to the spacecraft. It took 84 minutes, travelling at the speed of light, for those commands to cross the immense gulf between Earth and the Saturnian system.

Voyager 1 responded crisply, rotating its high-gain antenna away from Earth. Its hydrazine-fuelled thrusters hissed for almost 12 minutes, affording it a slight sideways nudge for the Titan flyby. The probe then realigned itself with our world. To everyone's immense relief, communications were restored 84 minutes later.

Investigations Begin

The first dividend was paid soon after. Early on 11 November, the spacecraft's radio signal passed through Titan's thick orange clouds, gradually faded and then vanished, reappearing after 13 minutes. The signal's 'occultation' allowed investigators to show that Titan's atmosphere — first detected spectroscopically in the 1940s — was far more substantial than anticipated. Later analysis of the signal data revealed the existence of a solid surface with a temperature of –180°C.

The radio signal also showed the moon to have an equatorial diameter of around 5,150km. This was a significant find as, until 1980, the unknown size of Titan's opaque veil had spawned the erroneous assumption that it was the biggest natural satellite in the Solar System, larger even than Jupiter's moon Ganymede. An occultation of our Moon, seen from Earth a few years earlier, suggested an optical size of 5,800km, but this figure was biased by a lack of precise detail regarding the thickness of Titan's clouds. With Voyager 1's data, it was possible to ascertain that Ganymede is marginally the larger of the two, and that both moons are bigger than the Solar System's innermost planet, Mercury.

Titan's equatorial tilt causes distinct seasons and Voyager 1 was able to show that gases and particulates migrate from one hemisphere to the other. Along with the sheer density of the atmosphere, this highlighted broad differences in albedo. Neither Voyager 1 nor Voyager 2, which swept 907,000km past Titan in August 1981, saw any trace of a solid surface through the murk, but they did identify a dark brown 'hood' of detached haze over the north pole. This contrasted starkly with the far brighter south and provided a glimpse of the seasonal variation — at the time it was spring in the north and autumn in the south.

The moon's atmosphere was known to contain methane long before the Voyager probes arrived, although it turns out that methane only accounts for a few per cent. In fact, protons from Saturn's fierce magnetosphere and ultraviolet photons from the solar wind separate molecules of nitrogen and methane. Their atoms recombine into a raft of trace constituents, including hydrogen cyanide and acetylene, many of which were detectable to the Voyagers' infrared instruments. Hydrogen cyanide plays an important role in the synthesis of amino acids and its discovery at Titan triggered early theories that the moon might harbour the building blocks for complex organic chemistry. Indeed, it may even mirror conditions on the infant Earth, as it was billions of years before life evolved here.

A Complicated Picture

During their rapid transits, the Voyagers observed cooler temperatures nearer the moon's and warmer ones in the high troposphere, a phenomenon known as 'temperature inversion'. It's driven primarily by ultraviolet sunlight and contributes to Titan's already complicated photochemical picture, which is dominated by a dense layer of hydrocarbon 'smog', 200km thick, whose particulates vary in size from 0.2µm to 1µm. Even in 1980, it was argued that these particulates could 'snow' onto Titan's surface, and so the existence of hydrocarbon lakes and seas was plausibly considered for the first time.

Eighteen hours after leaving Titan, Voyager 1 hurtled 64,200km past the sickly yellow cloud-tops of Saturn, the Solar System's most visually spectacular planet. Its intricate rings, which so puzzled Galileo in 1610, before they were correctly described and identified by Christiaan Huygens in 1655, have a radial breadth of 282,000km, equivalent to three-quarters of the distance but are believed to be no more than 1.4km thick.

Three rings, dubbed A, B and C, together with the 4,800km-wide Cassini Division, were known to astronomers long before the dawn of the Space Age. In September 1979, Pioneer 11 found the F ring, which resembled a contorted tangle of narrow strands. Moreover, its data hinted strongly at the possible existence of tiny 'moonlets', which somehow anchored, or 'shepherded', the ring material along its million-kilometre-long tracks. A year later, Voyager 1 discovered the moonlets Prometheus and Pandora, both of which straddled and possibly influenced the structure of the F ring. Unfortunately, a defective photopolarimeter meant that the probe was unable to examine them in great detail.

Still, Voyager 1 managed to locate the dusty D ring and the exceptionally slender G ring. Nine months later, Voyager 2 encountered Saturn with a fully functioning photopolarimeter and managed to resolve groups of hitherto-unseen 'ringlets', showing that very few gaps existed anywhere in the rings.

Even the notionally 'empty' Cassini Division, the broad, dark band of which separates the bright A and B rings, turned out to be populated by a vast mass of dust and rocky fragments. Radio-science measurements confirmed that the most closely spaced particles ranged in size from under 1cm to 10m or more.

The Rings' Origins

The principal constituent of the rings is water-ice. It makes up 99.9 per cent of the rings and is what makes them so dazzlingly reflective, although both Voyagers saw discoloration in places, perhaps due to the presence of impurities such as tholins or silicates. Until 1980, scientific consensus favoured gravitational forces as the driving force behind the rings' formation. Yet the Voyager probes uncovered radial features, including spokes and kinks that are inconsistent with gravitational orbital mechanics.

Voyager 1 took a sequence of images during one of Saturn's rotations that revealed the spokes' formation and dissipation lifecycles. The images showed them to be charged particles that levitated above the rings.

It had been argued that divisions within the rings were formed by the process of orbital 'resonance', whereby particles were confined to specific regions by the gravitational attraction of neighbouring shepherd moons. The discovery of Prometheus and Pandora lent credence to this idea, and particles bordering the Cassini Division are thought to be influenced by the presence of the moon Mimas.

Elsewhere, particles near the edge of the A ring are 'sharpened' by the moonlet Atlas — its astonishing equatorial ridge might represent a deposit of swept-up ring material — and by the co-orbiting moonlets Epimetheus and Janus.

Another moonlet, the walnut-shaped Pan, was found in 1990, following an analysis of old Voyager 2 images. It's thought to be responsible for 'scalloping' the edges of the 325km-wide Encke Gap in the A ring and keeping it free of particles. Still other openings in the rings — including the Cassini Division and the narrower Huygens Gap — are thought to be controlled in part by the influence of Mimas. Another gap, measuring 42km in diameter and named in honour of astronomer James Keeler, was detected by the Voyagers deep within the A ring.

Giant Storms

Unexpectedly, the composition of Saturn's atmosphere was quite distinct from Jupiter, with smaller helium abundances and a larger relative share of hydrogen — about 96 per cent, compared to the Jovian 87 per cent. Like its larger cousin, Saturn was shown to radiate more heat into space than it absorbed from incident sunlight and it rotates rapidly upon its axis, generating the polar flattening and outwardly bulging equator that's a curious characteristic of all four giants.

In a further contrast to Jupiter, Saturn is 30 per cent less massive, leading to the famous idiom that if a sufficiently large bathtub could be found, it might float on the water. Its latitudinal banding is also much less obvious. But the world whose name pays homage to the fabled father of Jupiter and Bringer of Old Age is by no means an inactive place. Half a century before the Voyagers visits, comedian and amateur astronomer Will Hay observed an elliptical white spot near Saturn's equator, one of several periodic sightings of large-scale storms at work.

When Voyager 2 flew past the planet on 25 August 1981, it revealed eastward-gusting jet-streams, which peaked at 1,800km/h — five times faster than those on Earth. Marginally greater winds were also clocked at higher latitudes. Data from both spacecraft uncovered powerful polar aurorae at latitudes above 65°N, together with ultraviolet emissions of hydrogen at mid-latitudes.

A Parting Gift

It was Pioneer 11 that first detected the unusual alignment of Saturn's magnetic field, which is tilted by less than 1° with respect to its rotational poles, while the Voyagers observed a strange 'torus' of positively charged hydrogen and oxygen ions about 400,000km above the cloud tops. The strong emissions associated with this torus were measured by the fields-and-particles instruments, revealed a million-kilometre-wide 'sheet' of plasma, perhaps supplied by atmospheric material from Saturn and Titan. The planet's magnetosphere is much smaller than the enormous cavity that encapsulates Jupiter, but was still shown to span over two million km by Voyager 1. Nine months later, when Voyager 2 arrived, solar wind pressures had heightened and markedly compressed the sunward boundary. Then, as the spacecraft departed Saturn on the outward leg of its journey, its instruments detected a sudden drop in solar wind pressure and the magnetosphere rapidly ballooned outwards in less than six hours.

It was a final parting gift. Then Voyager 2's instruments were deactivated and the spacecraft entered hibernation for its lonely, five-year trek to Uranus; the timing had almost been poetic. It seemed as if Saturn was bidding its visitors farewell, by offering up one more mystery to perplex and astound us.

Why Does Saturn Have Such Grand Rings?

For over three centuries, from the earliest observations by Galileo Galilei and Christiaan Huygens, Saturn was believed to be the only planet to have rings. More recently, its three giant cousins have revealed their own assemblages of dust and rocky grains. Despite being far less grandiose than those of Saturn, the creation and endurance of ring systems was a mystery it was hoped the Voyagers could help solve.

Two main theories took centre-stage before 1980. The first, by Edouard Roche, postulated that small moons residing at specific distances from a given planet would be torn apart by tidal forces and the debris might settle into rings. The second, by Pierre Laplace and Immanuel Kant, argued that the rings formed at the same time as Saturn, in a process similar to how the Solar System formed from a large disc.

As viewed by the Voyager probes, discrete particles in the rings were so bright and pristine — formed almost wholly water-ice, with some trace contaminants — that they seemed no older than a few hundred million years. Some particles are so small (from car-sized boulders to sand-like grains) that they would have been pulled into the atmosphere if they were much older than this. Furthermore, the Voyagers revealed exceptionally low levels of ambient radiation at Saturn, implying that the rings have thrived in a relatively benign environment.

This contributed to early theories that Jupiter, Uranus and Neptune lost their primordial gaseous discs quite early in their evolution, leaving mainly volatiles from which to assemble their far darker and less expansive ring systems. Saturn, on the other hand, cooled sufficiently early for water vapour to condense and eventually produce far more brilliant rings. During their encounters, the Voyagers also uncovered much more intricate detail, from spokes and kinks to ringlets and shepherd moons, than had been expected.

A Growing Moon Menagerie

Around a dozen moons were known to orbit Saturn before the Voyagers visited, the largest among them being the planet-sized Titan. Next largest was rocky Rhea, one-third the size at 1,530km in diameter.

It was Rhea — stripped of a 'sensible' atmosphere, globally crater-scarred and seen only from a great distance by both Voyager craft — that had endured two savage epochs of meteoroid bombardment in its youth. Those epochs are thought to have generated many craters on Saturn's other moons. Most intriguing are Tethys and Mimas, both predominantly water-ice, which showcase the biggest craters in proportion to their size ever seen. In fact, Mimas's Herschel crater (almost 10km deep and 130km across) covers a third of its diameter, so enormous that its causative impact must have almost broken the moon apart. Tethys boasts a shallower, more ancient feature, called Odysseus, which also spans a wide fraction of its terrain.

Then there's enigmatic Iapetus, which a bewildered Giovanni Cassini identified as 'two-toned' — bright on one face, dark on the other. The Voyagers revealed a meandering, 300km-wide transitional zone between the two halves, suggesting that preferential bombardment of Iapetus's leading hemisphere by darkened material could be responsible. Elsewhere, icy Enceladus reflects virtually all incident sunlight, rendering it the brightest-known natural satellite and raising early suspicions of 'cryovolcanism'. Rugged Dione was shown to possess a co-orbital companion moon, while potato-shaped Hyperion might be the remnant of an ancient collision and blob-like Phoebe could represent a seized asteroid.

With the Voyagers' close-range observations of Janus and Epimetheus, the floodgates opened. Three more moons (Atlas, Prometheus and Pandora) were found by the Voyagers and later Earth-based work on their imagery led to the detection of others, including Pan. Today, it's known that more than five dozen moons with confirmed orbits exist at Saturn, but the presence of innumerable particles within the rings — from grains to moonlets — could carry this figure into the thousands or beyond.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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Voyager: The 40-Year Space Journey

In 1977, two spacecraft left Earth to explore the gas and ice giants. On the anniversary of their departure, Jenny Winder charts their journey towards the edge of the Solar System

Artist's concept of Voyager in flight. By NASA/JPL [Public domain], via Wikimedia Commons

Forty years ago, in August and September 1977, NASA launched two spacecraft on an audacious mission that would eventually study all four giant outer planets and 48 of their moons, and go on to explore the outer reaches of our Solar System. Today, Voyager 1 is our most distant spacecraft, and in 2012 became the first to enter interstellar space. Voyager 2 isn't far behind; it's hoped that it too will 'go interstellar' in the next five years.

The origins of the mission hark back to 1965, when it was realised that a planetary alignment in the latter half of the 1970s would enable a spacecraft to make a complete survey of Jupiter, Saturn, Uranus, Neptune and Pluto. Such an alignment only occurs every 175 years — it was an opportunity not to be missed.

To make the most of it, NASA settled on two identical spacecraft to travel on two separate trajectories. Both would study Jupiter and Saturn. Voyager 1 would then go on to fly by Saturn's largest moon Titan. Voyager 2, meanwhile, would have the option to go to Uranus and Neptune, becoming the first spacecraft to visit either. Each planetary flyby would alter the spacecraft's flight path to deliver it onto the next planet and increase its velocity, reducing the flight time to Neptune from 30 years to just 12. Pluto was off the table; the choice was between it and Titan, and Titan was seen as a more interesting target.

Budget constraints meant the spacecraft were officially only built to last five years, with the hope that they would be able to complete the extended mission to Uranus and Neptune. They launched with 11 scientific instruments: four on Voyager 1 continue to send back data about its surroundings, while five remain operational on Voyager 2.

One of the instruments still active on both is the low-energy charged particle detector (LECP) instrument, which scans the sky through 360° every few tens of seconds measuring cosmic rays. That it continues to function is extraordinary, says its principal investigator, Dr Stamatios M Krimigis.

"The most remarkable design feature of LECP was the stepper motor," he says. "A mechanical device like this in space was frowned upon because everyone thought it could get stuck in short order. We tested the motor for about 500,000 steps, twice the expected usage and it survived. Now it's performed over seven million steps and counting."

Science data from the instruments is returned to Earth in real time via each probe's high-gain antenna. The signals are picked up by the Deep Space Network (DSN), a global spacecraft tracking system, which was also used to reprogram the spacecraft remotely on more than one occasion. Travelling too far from the Sun for solar panels to be employed, the probes rely on three radioisotope thermoelectric generators for power. These convert heat produced from the radioactive decay of plutonium into electricity.

Messages for ET

Each spacecraft also carries a message from humanity in the form of a 12-inch gold-plated copper record. The cover for the Golden Records bear diagrams explaining how to play them, showing the location of our Sun and the two lowest states of the hydrogen atom as a fundamental clock reference.

The selection of content for the record, by a committee chaired by Carl Sagan, was completed in six weeks, chosen to portray the diversity of life and culture on Earth. There are spoken greetings in 55 languages; 116 images; recordings of natural sounds; music from Bach, a Navajo Indian song, Azerbaijani folk music and Chuck Berry; and even a recording of the brainwaves of Ann Druyan, the creative director of the project.

Voyager 1 was launched two weeks after Voyager 2, but on a shorter and faster trajectory that would see it overtake its twin and reach Jupiter first. Between January and August 1979, the Voyagers studied the Jovian system. They revealed Jupiter's famous Great Red Spot to be a complex anticyclonic storm, found smaller storms throughout the planet's clouds and saw flashes of lightning in the atmosphere on the night side. Jupiter's faint, dusty rings were also discovered, along with the satellites Adrastea, Metis and Thebe. But the highlight of the Jupiter mission was the discovery of active volcanism on the moon Io. Together, the Voyagers observed the eruption of no fewer than nine volcanoes on Io. "At that time, the only known active volcanoes in the Solar System were here on Earth, and here was a moon, just a moon of Jupiter, that had 10 times more volcanic activity than here on Earth," explains Voyager project scientist Ed Stone, who has been with the mission from the start. The Voyagers also found Io was shedding a thick torus of ionised sulphur and oxygen, and revealed evidence for an ocean beneath the icy crust of Jupiter's moon Europa.

At Saturn, they studied the planet's complex rings and its atmosphere, and found aurorae at polar latitudes and aurora-like emissions of ultraviolet hydrogen at mid latitudes. They measured Titan's mass, studied its thick nitrogen atmosphere and imaged 17 of Saturn's moons, including three new discoveries: Atlas, Prometheus and Pandora.

From there the two probes parted company as Voyager 1 began its long journey out of the Solar System. Voyager 2 headed to Uranus, where it discovered 11 new moons and visited 16. It discovered the planet's magnetic field and studied the ring system. At Neptune Voyager 2 discovered storms, including the Great Dark Spot, and 1,600km/h winds — the strongest on any planet. It imaged eight of Neptune's moons, discovering five of them and saw active geysers on the largest moon, Triton.

One last glimpse

On Valentine's Day 1990, Voyager 1 took the final pictures of the mission. Turning its camera back towards the Sun, from about 6 billion km away, it took images of Neptune, Uranus, Saturn, Jupiter, Venus and — suspended in a beam of sunlight — the now famous 'Pale Blue Dot' image of Earth. Carolyn Porco planned and executed this Family Portrait alongside Carl Sagan. "As soon as I joined the Voyager imaging team in fall 1983, the idea arose in my mind to take an image of the planets, but especially Earth, as they would be seen from far away, to force that 'reckoning' that comes from seeing our cosmic place as it really is ... alone and isolated," she says.

This marked the end of the Voyagers' planetary explorations — the Grand Tour, as it's known — and the beginning of the Interstellar Mission. In 1998, Voyager 1 overtook Pioneer 10 to become the most distant spacecraft from the Sun. Voyager 2 is expected to pass Pioneer 10 by April 2019.

In December 2004, Voyager 1 crossed the termination shock, marked by a massive drop in particles detected from the Sun and a rise in cosmic ray particles. Voyager 2 followed in August 2007. Finally, on 25 August 2012, at 121 AU from the Sun, Voyager 1 officially crossed into interstellar space.

The Voyager team is still listening. "We listen every day, for four to eight hours per day, per spacecraft, and we'll continue to do that as long as they are sending us something new to learn," explains Ed Stone. From 2020, however, the remaining instruments will be switched off one by one to conserve power. It's hoped they will fly for at least 10 more years. "My goal is to have a 50th anniversary party for Voyager," says Suzanne Dodd, project manager of the Voyager Interstellar Mission.

Stone considers the Voyagers to be "our silent ambassadors". In 40,000 years, they will each pass 1.5 lightyears from stars in Andromeda and Camelopardalis. Having increased our knowledge of our solar neighborhood, the Voyagers will take the story of Earth on to other star systems.

Voyager Mission Timeline

On their long travels, the Voyagers visited four planets and imaged 48 moons. Now they are at the very edge of the Solar System.

20 August 1977
Voyager 2 launches from Cape Canaveral at 14:29 UT atop a Titan IIIE-Centaur launch vehicle

5 September 1977
Voyager 1 launches at 12:56 UT from Cape Canaveral also atop a Titan IIIE-Centaur

10 December 1977
Voyager 2 enters the asteroid belt, swiftly followed by Voyager 1

19 December 1977
Voyager 1 overtakes its twin, placing it on course to reach Jupiter first

8 September 1978
Voyager 1 exits the asteroid belt and continues on to Jupiter

21 October 1978
On a slower trajectory, Voyager 2 finally exits the asteroid belt

5 March 1979
Voyager 1 makes its closest approach to Jupiter

9 July 1979
Voyager 2 makes its closest approach to Jupiter

12 November 1980
Voyager 1 flies by Titan and Saturn, then begins its journey out of the Solar System

25 August 1981
Voyager 2 flies by Saturn but remains within the plane of the planets, bound for Uranus

24 January 1986
Voyager 2 has the first-ever encounter with Uranus, revealing a bland visible surface

25 August 1989
Voyager 2 is the first probe to observe Neptune, a stormier planet than its neighbor

14 February 1990
Voyager 1 takes the Pale Blue Dot image of Earth from 6 billion km away

17 February 1998
Voyager 1 becomes the most distant human-made object in space

17 December 2004
Voyager 1 passes the termination shock and enters the heliosheath

30 August 2007
Voyager 2 passes the termination shock and enters the heliosheath

25 August 2012
Voyager 1 crosses the heliopause and enters interstellar space

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

The Unknown Realm of the Ice Giants: Uncharted Territory — Uranus & Neptune

In January 1986 and August 1989, Voyager 2 flew past the outer giants Uranus and Neptune — becoming the first spacecraft to visit either. In its brief visits, these cold worlds almost beyond the reach of the Sun's warmth were revealed to be every bit as mysterious as their closer cousins.

Uranus as seen by NASA's Voyager 2. By NASA (http://photojournal.jpl.nasa.gov/catalog/PIA18182) [Public domain], via Wikimedia Commons

Perhaps the toughest kind of exploration is studying a pair of planets about which virtually nothing is known with certainty. In February 1984, several dozen scientists gathered in Pasadena, California, to consider the scant level of knowledge about Uranus and Neptune. These two giants, which reside on the fringe of our planetary system, had only been discovered in the preceding two centuries. And as Voyager 2 journeyed towards them for humanity's first-ever visits, neither had revealed itself as much more than a fuzzy blob in an ocean of emptiness.

Worth a visit

The desire to travel to Uranus and Neptune originated with NASA's Grand Tour programme, but a subsequent rescoping of the mission led to a revised focus on Jupiter and Saturn. Nevertheless, in 1976 NASA approved an extension to Uranus on the condition that all primary objectives were met. A modified infrared detector was built to achieve the necessary resolution at Uranian distance — 2.6 billion km from Earth — but when the Uranus flyby formally began it did so with a greatly reduced budget and a leaner workforce.

By that time Uranus was known to possess five moons, named after characters from the works of William Shakespeare and Alexander Pope. The first pair, Titania and Oberon, were found in 1787 by Uranus's own discoverer, William Herschel, with Ariel and Umbriel observed by William Lassell in 1851 and tiny Miranda identified by Gerard Kuiper in 1948. Some 1.6 billion km beyond Uranus, Neptune was attended by Triton and Nereid, fittingly named after classical deities of the sea. All were barely detectable with Earth-based instruments before the Voyager 2 probe arrived.

Following Uranus's discovery in 1781 and the finding of Neptune thanks to the mathematical predictions and telescopic observations of Johann Galle, Urbain Le Verrier and John Couch Adams in 1846, there existed only the most general and sweeping awareness of either planet. They were known to be near-twins in size, with equatorial diameters around 50,000km, four times bigger than Earth and over 15 times more massive. The probe confirmed hydrogen and helium as their predominant constituents. Uranus's plain aquamarine colour and the richer, sky-blue façade of Neptune also betrayed the presence of ammonia, methane and hydrogen sulphide.

Data gathering

Travelling at 64,000km/h, Voyager 2 had only six hours on 24 January 1986 to make its close-range observations of Uranus. But to maximise the scientific yield of its flyby, the probe took measurements of the planet continually for 16 weeks from November 1985 until February 1986. A similar campaign was adopted at Neptune from June to October 1989. "We had a prediction of where the spacecraft would be at each point in time," recalled Voyager imaging team member Andrew Ingersoll. "We told the engineers what latitude and longitude we wanted to look at and they told the camera to take a picture. These commands had to be worked out and radioed to the probe weeks in advance."

Due to Uranus's 98° axial tilt, Voyager 2 approached the planet's sunward-facing south pole and generated time-lapse movies to track cloud movements and wind speeds. Unlike on Jupiter and Saturn, there was little evidence of storms or latitudinal banding, which led the imaging team to wryly dub themselves 'the imagining team'. However, infrared data revealed clouds beneath a high-altitude layer of hydrocarbons and the probe's radio-science and ultraviolet instruments revealed uniform temperatures throughout the atmosphere of around -216°C.

Theories abounded that this atmosphere might extend more than 3,000km beneath the cloud tops, perhaps terminating in a slushy ocean of water, ammonia and methane, girdling an Earth-sized rocky core. A similar situation is also thought to exist at Neptune. Voyager 2 was unable to prove the existence of such oceans, but did detect radio signals induced by interactions between the solar wind and electrons in the planets' magnetic fields. This enabled its magnetometer to measure Uranus's day at 17.25 hours and Neptune's day at 16.1 hours, which in turn helped provide wind-speed estimates.

The dark of the moons

To great surprise, Uranus's magnetic field extended only 600,000km sunward, but wound backwards, like a giant corkscrew, 10 million km beyond the planet. Ultraviolet observations of polar aurorae showed that the field was tilted at 59° to Uranus's rotational axis — a curiosity that, on Earth, would be equivalent to having our north magnetic pole in the Florida Keys — and bore a powerful sting in the guise of trapped, high-energy radiation. This clearly manifested itself on the surfaces of Uranus's moons.

All five moons appeared intrinsically dark, suggesting that radiation had broken down any methane on their surfaces within a few tens of millions of years, darkening them and leaving a thick, charcoal-like dusting. Umbriel is by far the darkest, although it does exhibit a few splotches of bright material, including an enigmatic 'Cheerio' in the crater Wunda at its equator. As for its siblings, Titania — the largest, at 1,580km across — is marred by huge faults and winding canyons, pointing to a violent tectonic past. Oberon revealed bright and dark regions, not unlike our Moon, indicating meteoroid bombardment and perhaps the volcanic extrusion of subsurface material.

But it was Miranda and Ariel to which Voyager 2 devoted the most attention. The latter is the brightest Uranian moon, with an ancient and heavily cratered terrain that features rolling plains, parallel ridges and troughs lying tens of kilometres apart. Miranda, less than 500km in diameter, was the most closely inspected, principally due to the flyby geometry needed by Voyager 2 to reach Neptune.

It revealed unmistakable evidence of billions of years of impacts, which tore Miranda apart, then hammered it back together, gouging out 20km-deep canyons, at least three enormous, oval-shaped 'coronae' and broad terraces of old and young, bright and dark, lightly and heavily cratered terrain. One area, the 200km-wide Inverness Corona, showed a bright chevron-like feature between dark layers, possibly a result of reaggregated bits of Miranda's original crust, poking out from the present surface.

New moons

Voyager 2 also found 10 new moons, ranging from 160km-wide Puck to diminutive Cordelia, about an eighth as large. A small subset that share similar orbits, surface colouration and generally elongated shapes was classified as the 'Portia Group' (named for its biggest member). Another object was photographed by the probe, but went unrecognised as a moon until 1999. It was fittingly named 'Perdita', the Latin word for lost.

Something that had already been seen at Saturn was the pivotal role tiny 'shepherd' moons play in anchoring ring material. Several narrow rings had been detected around Uranus by ground-based observers in the 1970s, but Voyager 2 uncovered another pair. The probe revealed the new pair to be relatively insubstantial, although the brighter 'Epsilon ring' achieved a maximum extent of 96km.

Up to 18 shepherd moons were predicted to exist at Uranus, but only two — Cordelia and Ophelia — were detected, lying astride and 'binding' the inner and outer edges of the Epsilon ring. The general darkness of the rings underscores their extreme youth, for they are probably no more than 600 million years old. Data from Voyager 2's photopolarimeter and other instruments revealed them to be so sharp that the Epsilon component can't be greater than 150m thick.

Rings were also eagerly anticipated at Neptune, with ground-based studies between 1968 and the early 1980s suggesting that incomplete 'arcs' might run part-way around the planet. Numerous theories postulated that the arcs were held in place by tiny shepherd moons or maybe new rings were in the process of forming. With just two weeks to go until Voyager 2's arrival, their true nature was revealed. A pair of incomplete arcs did appear to exist, with three shepherd moons (Galatea, Larissa and Despina) interacting with them.

Building rings

As the probe drew nearer, it became apparent that more rings extended around the planet. Their uneven 'clumpiness' and irregularly distributed particles offered an early explanation for why arcs had been suspected for so long. Indeed, Neptune's outermost 'Adams' ring revealed several clods of material, up to 50km wide. It was argued that debris from ancient moons could have contributed to this unequal distribution of mass and a pair of tiny moons, Thalassa and Naiad, could themselves someday be torn apart and incorporated into the system.

Voyager 2 confirmed the existence of six new moons at Neptune, including potato-shaped and heavily cratered Proteus, which is thought to be almost big enough for gravity to pull it into a spherical shape. Eccentric-orbiting Nereid, discovered by Gerard Kuiper in 1949, was also seen by the probe, but at a distance of 4.7 million km it was still too far away to resolve any surface detail, much less measure its rotational characteristics.

Before it found any rings, it was hoped that Voyager 2 would fly within 10,000km of the planet's largest moon, Triton, which ground-based observations had shown to possess nitrogen ices on its surface. To avoid the risk of colliding with ring particles, the probe's trajectory was altered to carry it 4,950km over Neptune's north pole — the closest planetary encounter achieved by either Voyager craft — on 25 August 1989. It then plunged south, passing within 39,800km of Triton, five hours later.

Circling Neptune in a highly inclined 'retrograde' orbit, the moon proved smaller than predicted, at just 2,700km across, and a stellar occultation allowed Voyager 2 to measure its 800km-deep atmosphere, all the way down to its surface, the coldest known in the Solar System at a frigid -236°C. In fact, Triton's tenuous mix of gases and particulates is virtually a vacuum, barely capable of supporting thin nitrogen-ice clouds and haze at an altitude of 13km.

Voyager 2 strongly hinted that these constituents originated from the evaporation of surface ices, with winds transporting dust particles up to 50km across its terrain. Triton is the most spectroscopically diverse object in the Solar System, reflecting over 85 per cent of incident sunlight — eight times more than our Moon — and this extreme brightness was a key reason why such a tiny, distant body was found telescopically by William Lassell in October 1846, just weeks after Neptune itself.

Freeze-thaw effect

The probe imaged a third of Triton's surface, uncovering a greenish landscape, nicknamed 'cantaloupe', due to its similarity to the scaly skinned melon. It was crisscrossed with circular depressions, each around 25km wide, and long, interconnecting ridges were thought to be the result of epochs of melting and refreezing. This reinforced the notion of Triton as a captured Kuiper Belt object and that the tidal heating from Neptune's gravity had left its interior fluid for a billion years, underpinning these complex internal processes.

Voyager 2 also revealed a pinkish southern polar cap, abutted by a blue-tinged crustal region, indicative of the presence of methane, nitrogen and water ices. And it was from within the polar caps that a moderate greenhouse effect could have been nurtured, forcing exotic ices to 'de-gas' and build pressure, before prompting one of the most surprising discoveries at Triton: erupting geysers.

In August 1989, only Earth and Jupiter's moon, Io, were known to harbour active volcanism, but dark streaks across Triton's southern polar cap indicated that such phenomena were commonplace, even in this far-flung corner of the Solar System. One geyser was observed to hurl carbonaceous material to an altitude of several thousand metres, while other measurements allowed local wind speeds to be clocked at 54km/h, as strong as a moderate gale on Earth.

Providing a backdrop to these discoveries was magnificent Neptune itself, whose outward similarity to Uranus belied a far more active world. Despite its greater distance from the Sun, infrared data showed it to radiate 2.6 times as much heat from incident sunlight as Uranus. And although the near-twins are thought to have similar compositions, Neptune is marginally more massive, which influences its magnetic field and internal heat. "Wow," exulted one planetary scientist, breathlessly, as Voyager 2 became the only spacecraft in history to visit four planets. "What a way to leave the Solar System!"

Beefing up the Voyagers from the ground

Orbiting billions of kilometers beyond Saturn, the outer giants Uranus and Neptune inhabit a gloomy region of the Solar System, requiring Voyager 2 to examine worlds where high noon is dimmer than dusk on Earth. One scientist likened the problem to photographing a pile of charcoal briquettes lying at the foot of a Christmas tree, lit by a single-Watt bulb.

Stability was crucial, but even turning its tape recorder on and off was enough to induce a disruptive 'nodding' effect in Voyager 2. Its gyroscopes could keep the instruments reasonably steady, but engineers had to halve the duration of thruster firings to allow the probe to settle after manoeuvres. At Neptune, longer exposures of 96 seconds and thruster firings under four milliseconds became necessary. Image motion compensation allowed Voyager 2 to resolve finer detail, but at the expense of picking out irritating optical flaws, including dust on its lenses.

Back on Earth, the three tracking stations that make up NASA's Deep Space Network (located in Canberra, Australia, the remote foothills west of Madrid in Spain and in California's Mojave Desert) received a $100 million facelift to boost Voyager 2's ever-weakening signal, which by January 1986 was a billion times fainter than a watch battery. All three stations had their 64m antennas augmented for Uranus, electronically synchronising them to strengthen the signal. Further upgrades to 70m were implemented for Neptune and two additional tracking stations in Japan and New Mexico were called into duty.

Due to the position of Uranus in Earth's skies in the winter of 1985-1986, Canberra was the main tracking station, following Voyager 2 for 12 hours per day and allowing a 21.6kbps downlink rate. In support, a 400km microwave connection was established with the Parkes radio telescope in New South Wales, bolstering it by 25 per cent and allowing up to 50 extra photographs to be returned every day.

The Bullseye Planet

Uranus is unique among the planets in our Solar System thanks to its extraordinary rotational tilt of 98° — Uranus presents itself to observers as a world tipped on its side. Its poles lie where its equator should be and receive a correspondingly higher level of incident sunlight. Situated 2.8 billion km from the Sun, Uranus circles its parent star every 84 years, with each pole rhythmically illuminated, before being plunged into frigid darkness, every four decades.

When Voyager 2 viewed the planet only the southern pole was in direct sunlight. Its five main moons orbit their giant host within its equatorial plane, placing their southern halves at the height of Uranian summer in January 1986 and casting their northern extremities into a 21-year-long winter season.

How Uranus's axial tilt came about remains a mystery, although a collision with an Earth-sized impactor has been proposed. The fact that the moons circle within its equatorial plane implies that they formed much later from debris placed into orbit by this impact. Moreover, Uranus radiates hardly any heat into space — its temperatures dip as low as -224°C, giving it the coldest planetary atmosphere in the Solar System — and it's possible that whatever hit the planet caused it to expel much of its primordial heat.

A World Of Wild Weather

Four-and-a-half billion kilometres from its parent star, recipient of half as much sunlight as gloomy Uranus and with temperatures as low as -218°C, Neptune should be an inactive world. Yet Voyager 2 revealed it to be surprisingly energetic, with the oval-shaped Great Dark Spot observed at a latitude of 22°S. This counter-clockwise-rotating vortex bore many uncanny parallels with Jupiter's Great Red Spot, in terms of relative size, motion and position within the atmosphere.

As the probe drew closer, a second, smaller dark spot was found, together with a chevron-shaped, westward-moving cloud feature, whose rapid 16-hour transit around Neptune's atmosphere generated the nickname of 'Scooter'. The Great Dark Spot, in keeping with its name, was 10 per cent darker than its surroundings and hustled northwards through the atmosphere at 1,100km/h. At its edge was a hovering, shape-shifting 'bright companion' cloud. The spot lay 50km below Neptune's main cloud deck, with the companion at a slightly higher altitude, creating analogies with lenticular cloud formations on Earth.

Elsewhere in the sky-blue atmosphere were cirrus streaks of methane-ice, which cast shadows, tens of kilometres long, on Neptune's cloud deck at low northern latitudes. How such wild weather can manifest itself on such a cold planet must be related to its dense interior and the fact that it emits 2.6 times as much heat as it receives from incident sunlight. It has been suggested that temperature differences between Neptune's internal heat and its cold atmosphere could trigger instabilities and induce large-scale meteorological phenomena.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Missions of the Future

With a fleet of probes being readied for flight over the next few years, Elizabeth Pearson looks at the destinations these missions will be heading to throughout our Solar System, as well as what they hope to uncover

Image from Pixabay courtesy of Andrew-Art, Space probe and Jupiter

Mercury

Only two spacecraft have ever been sent to the innermost planet of our Solar System, but that number is set to double. Two probes will fly to Mercury together as part of the BepiColombo mission, due for launch in 2018: ESA's Mercury Planet Orbiter and JAXA's Mercury Magnetospheric Orbiter. These two spacecraft will work together to provide a complete study of the planet's geology, composition, structure and interior when it arrives at the planet in 2024. The aim is to understand Mercury's place in our Solar System's creation and history. One of the greatest mysteries the two the probes will address is that of planet's magnetic field, first detected by Mariner 10 in 1974.

Mercury should be too small to host a molten core, thought to drive the magnetic fields of other planets; uncovering the interior of this world will help clarify which planets are capable of hosting a magnetosphere, both in this planetary system and beyond.

The Moon

Since the early days of the Space Race, reaching the Moon has been a symbol of a country's prowess as a spacefaring nation. But with NASA's eyes on Mars and Russia's lunar exploration programme suspended until 2025, it's time for new players in the space game to join the ranks of lunar explorers.

Both China and India have already conducted lunar missions and both are planning on building on their successes. Chang'e 5 will continue the China National Space Administration's (CNSA's) robotic exploration of the Moon in 2017, and return up to 2kg of material to the Earth — the first fresh lunar samples since 1976.

Set to launch in 2019, another Chinese mission, Chang'e 4, was initially intended as a back up to Chang'e 3. Following that mission's success it was reconfigured to land on the far side of the Moon, an area that has never been visited. The Indian Space Research Organisation (ISRO) is also hoping to cement its spacefaring credentials with the Chandrayaan-2 mission in 2018. The mission will land a rover on the lunar surface — the nation's first attempt touch down on another world.

But the days of space agencies holding sole claim to the Moon could be about to change, as a fleet of private companies are in the final leg of their own race to the lunar surface. The Google Lunar X Prize challenged private groups to land a rover on the Moon by the end of 2017. Three companies have arranged launch contracts so far. After many years of silence, the lunar surface is about to get a lot busier.

Mars

The Red Planet has had its fair share of visitors in recent years, a trend that will continue for the next decade as several new missions head for Mars.

NASA will continue its long legacy of Martian exploration with the InSight (Interior Exploration using the Seismic Investigations, Geodesy and Heat Transport)mission due for launch in 2018. It is a stationary lander that will measure the planet's seismological and thermal activity to work out what's going on under Mars's crust.

In 2020, not one but two new rovers will launch for the Red Planet — NASA's Mars 2020 rover and the second phase of ESA's ExoMars mission, which began in 2016 with the Trace Gas Orbiter. Both of these missions will look for signs of life, past and present, and try to determine if Mars was ever habitable.

But the time of robotic dominion over Mars could soon be at an end, as several key players are beginning to make real moves towards landing humans on the Martian surface. Both Chinese and US officials have stated a desire to start crewed missions to Mars over the next few decades. However, it might not be a government agency to put the first person on Mars, but a commercial one. SpaceX has always been vocal about its intention not only to launch a manned Mars mission, but also to set up a permanent base there. As a first step the company plan to fly and land a modified version of the Dragon module, currently used to send supplies to the International Space Station. This robotic mission, slated for 2018, could be a first step towards the century long journey of making humankind a multi-planet species.

Asteroids

The rubble of our Solar System's formation survives all around in the form of asteroids. Though mostly found in the asteroid belt, there are hundreds of these space rocks that regularly cross Earth's orbit, making them a tempting target for study.

Two missions to visit these cosmic wanderers are already underway, and both hope to return samples to Earth. JAXA's Hayabusa-2 spacecraft launched in 2014, bound for asteroid 162173 Ryugu. Once the probe arrives in 2018 it will obtain three samples, one of which will be excavated using an explosive charge, returning them in 2020. Its launch was followed by NASA's OSIRIS-REX, which set off for asteroid 101955 Bennu in 2016. Once there it will use gas jets to blast dust and rock off the surface before returning them home in 2023.

But robotic missions can only do so much, and NASA is currently planning an audacious mission to send humans to one of our rocky neighbours. The Asteroid Redirect Mission (ARM) will send a robotic probe to a near-Earth asteroid in the 2020s, retrieving a boulder weighing several tons from its surface and transferring it to Earth orbit.

From there, NASA will stage a series of manned missions to the boulder using the Orion crew module, which itself is still in development and hopes to fly in 2021.

This would be the first time such studies have been performed on the primordial bodies in space, rather than being returned to Earth. The mission would also provide a test bed for technologies that could one day take humanity deeper into the Solar System. Asteroids may prove a vital part of such endeavors, as mining them could provide raw materials for building spacecraft in orbit, as well as water. This could can be split into hydrogen and oxygen, and used in rocket fuel.

The Outer Solar System

The Solar System beyond the asteroid belt has remained relatively unexplored since the Voyager probes passed through three decades ago. But the giants of the outer Solar System will soon be giving up their secrets, as several missions to visit this mysterious region are planned. Juno is in the process of mapping out the largest of the gas giants, Jupiter, but it is this planet's companions that will be the next targets.

ESA's first mission to Jupiter, the Jupiter Icy Moons Explorer (JUICE) is currently being designed to make detailed observations of not only the planet, but three of the Galilean moons — Ganymede, Callisto and Europa. All of these worlds could potentially host liquid water oceans beneath an icy crust, making them the likeliest places to discover life beyond Earth. Aiming for a 2022 launch date, JUICE will find out not only if such oceans exist, but how they came to be and how likely it is that such moons are habitable.

Meanwhile NASA is planning a mission for the late 2020s that will perform multiple flybys of Europa, to help us understand its geology. Still in the concept phase, there is the potential for a lander, but it would not be capable of tunnelling through the several kilometers of ice to reach the subsurface ocean. Luckily, the Hubble Space Telescope has spotted jets of water shooting hundreds of kilometers above the moon's crust. If the main probe could fly through one of these, it could take a sample that originated deep within the moon.

NASA plans to venture even further into the outer reaches with its following mission — to Uranus. Currently under consultation, the spacecraft would orbit around the planet, which hasn't been visited in over three decades. Back then, Voyager 2 gave us only a handful of images of a seemingly placid world. Though it's unlikely we will see such a mission before the 2030s, it's worth the wait to see what Uranus hides beneath this calm exterior.

Beyond the Solar System

Though much of the focus of future space missions is on the planets around us, there is a much wider Universe waiting to be explored.

Exoplanets are one of the hottest research topics at the moment and there are several new observatories on the way. NASA's Transiting Exoplanet Survey Satellite (TESS) has already been built, ready for launch later in 2017. It will search the whole sky for exoplanets, but its main aim is to track down Earth-sized planets around nearby bright stars. Once found, those similar to our own world would be prime targets for follow up study by the Characterising Exoplanet Satellite (CHEOPS), which ESA is building for a 2018 launch. Looking at already known exoplanets, CHEOPS will be able to determine their precise orbital properties and radii.

The next goal will be to understand the atmosphere that surrounds these worlds. The UK-built Twinkle satellite, which has just finished its design phase and is planned to launch in 2019. Its aim is to capture the 0.01 per cent of starlight that shines through an exoplanet's atmosphere, which can then be untangled to reveal what chemicals compose it. Perhaps the most anticipated tool in the exploration of exoplanets, however, is the James Webb Space Telescope. From 2018 onwards, this amazing infrared telescope could be used to look at these distant planetary atmospheres, and will be able to do much more besides. Touted as the Hubble Space Telescope's successor, the JWST will be able to study everything from the origin of the Solar System to the first light that ever shone in the Universe.

ESA plans to extend its own cosmic vision with the construction of two deep space observatories — Euclid in 2020 and Athena in 2028. These will help to identify the structure and geometry that govern our Universe, and to unlock the answers of how the cosmos we know came to be.

Future missions at a glance

There are dozens of missions set to take flight in the next decade, but where will they be headed?

2017:

Chang'e 5
Type: Lunar lander
Goal: Sample return

TESS
Type: Satellite
Goal: Exoplanet search

Google Lunar X Prize candidates
Type: Lunar lander and rover
Goal: Dependant on winner

2018:

BepiColombo
Type: Mercury orbiter
Goal: Geological and magnetospheric survey

Hayabusa-2
Type: Orbiter
Goal: Asteroid sample-return mission

OSIRIS-REX
Type: Orbiter
Goal: Asteroid sample-return mission

CHEOPS
Type: Satellite
Goal: Exoplanet measurement

InSight
Type: Mars lander
Goal: Seismic and geological survey

James Webb Space Telescope (JWST)
Type: Space observatory
Goal: Infrared imaging

Red Dragon
Type: Spacecraft
Goal: Test flight to Mars

Chandrayaan-2
Type: Lunar orbiter, lander and rover
Goal: Mineralogical and geological survey

2019:

Chang'e 4
Type: Lunar lander and rover
Goal: Mineralogical and geological survey

2020:

Mars 2020
Type: Mars rover
Goal: Habitability search

ExoMars 2020
Type: Mars rover
Goal: Habitability search

Euclid
Type: Space observatory
Goal: Observing the early Universe

2021:

Juice
Type: Orbiter
Goal: Observe Gallilean satellites at Jupiter

Plato
Type: Satellite
Goal: Exoplanet characterisation

Europa Clipper
Type: Orbiter
Goal: Habitability study of Europa

Athena
Type: Space observatory
Goal: X-ray imaging

Neptune Orbiter Mission
Type: Orbiter
Goal: Planetary observation

Arm
Type: Crewed
Goal: Redirect and survey asteroid

ABOUT THE WRITER
Dr. Elizabeth Pearson is BBC Sky at Night Magazine's news editor. She has a PhD in extragalactic astronomy.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Returning to Venus

Space Probes have helped us build a good picture of Mars, yet Earth's inner neighbor Venus is still very much a mystery. But, writes Paul Sutherland, a host of new missions are being planned to help us learn more about it.

Image by Anna M., Venus Transit

Nothing was known about the surface of Venus before the Space Age because it is completely obscured by clouds. Scientists once speculated that it might be a raging ocean, or a Sahara-like desert. The first probe to provide answers was NASA's Mariner 2, which flew past Venus in December 1962, discovering that surface temperatures must be extremely high and that, like Uranus, it rotates in the opposite direction to the rest of the planets in the Solar System. Since then, orbiting probes with cloud-piercing radar have produced maps of Venus's surface and Soviet landers have confirmed that conditions are completely inhospitable on the ground. There is neither sea nor desert, but rather a landscape resembling a vision of hell.

Fire and Brimstone

The surface temperature is twice the maximum found in a kitchen oven and the pressure of the poisonous atmosphere is 90 times that at sea level on Earth, which crushed probes making early landing attempts. The first Soviet probe to reach the surface and send back signals was Venera 7 in 1970, which survived for 23 minutes. It was followed by the more successful Venera 8 in 1972, which returned data on the surface temperature and pressure, wind speed and illumination, before being destroyed after 63 minutes. The probes had to be built like submersibles to withstand the air pressure, but their electronics quickly failed in the extreme heat. Subsequent Soviet landers in the 1970s and 1980s sent back crude photos of a rocky landscape.

Helium balloons were released into Venus's higher, cooler atmosphere in June 1985 by two Soviet Vega probes that were on their way to Halley's Comet. They gathered data for 47 hours each as they floated 50km high in the cooler clouds.

NASA's Mariner 10 flew past Venus in 1974 en route to Mercury and managed to image wind patterns in the clouds. This was followed by a dedicated US mission, Pioneer Venus, made up of two spacecraft that arrived in December 1978. An orbiter studied the atmosphere and made radar maps of the surface. The other component was a multiprobe made up of a transporter and four separate probes that were fired into the atmosphere, returning data for an hour.

NASA's next mission, Magellan, carried out extensive radar imaging of Venus from a polar orbit in the early 1990s. Its imaging of almost the entire surface revealed it was covered with volcanoes. Scientists suspect many are still active, but still no one can say for certain.

ESA's first envoy, Venus Express, was launched in November 2005. During the eight-year mission, the spacecraft's swooping orbit brought it low over the cloud tops and revealed big variations in the sulfur dioxide content, suggesting that the volcanoes were still active. Its fuel exhausted, Venus Express was purposefully destroyed in the atmosphere in early 2015.

A Japanese space probe called Akatsuki, launched towards Venus in 2010, looked lost after a fault caused it to fly past the planet. But five years later, mission controllers managed to rescue it and put it into a new, more elongated orbit where it began to survey the atmosphere.

Two NASA missions to the outer planets also gathered data on Venus as they flew past to get a gravitational boost on their long journeys. Galileo shot past on its way to Jupiter in February 1990, taking pictures, measuring dust, charged particles and magnetism, and making infrared studies of the lower atmosphere. Saturn probe Cassini made two flybys in April 1998 and April 1999 when it looked for, but failed to spot, lightning in the clouds.

The Trouble with Landers

Current proposals for future Venus missions are focusing on orbiters and a new generation of balloons and aerial vehicles. Experts see too many difficulties in sending a lander to explore the surface like the Martian rovers. As planetary scientist and Venus expert Dr. Colin Wilson of the University of Oxford explains: "The issue is the heat, because silicon electronics simply don't work at these temperatures. There are studies into building a new kind of electronics using silicon carbide — this is of interest also for use inside car engines and jet engines — but even if you sort that out, you still have the problem of how you are going to power a probe on the surface. Although Venus is closer to the Sun, only one or two per cent of the sunlight at the cloud tops reaches the surface and so solar panels are completely impractical. Radioactive power sources have been suggested, but this would make the mission both expensive and difficult."

Two proposals to explore Venus are on a shortlist of five Solar System projects currently being considered for the next round of NASA's Discovery Program, missions that could launch in the early 2020s. One, called DAVINCI (Deep Atmosphere Venus Investigation of Noble Gases, Chemistry and Imaging) is being studied by NASA's Goddard Space Flight Center. It is an entry probe designed to study conditions between the dense cloud tops and the surface. "It will have much more modern and accurate instrumentation than previous probes," says Wilson. "All their temperature sensors failed in the lower atmosphere so we have hardly any data about atmospheric processes near the surface. DAVINCI is really going to give us a much better understanding of the deep atmosphere of Venus, in particular of its chemistry." The other proposal, from NASA's Jet Propulsion Laboratory, is for a new orbiter called VERITAS (Venus Emissivity, Radio Science, InSAR, Topography and Spectroscopy) that aims to produce radar maps of the planet in much higher resolution than before. It has strong European support, including for a French-German infrared camera that will look for hot volcanic material on the surface.

Looking Further Ahead

But a further attempt to get a new spacecraft to Venus will come with a UK-led proposal to ESA for a mission called EnVision. The probe will be another orbiter with advanced radar to detect tiny changes in surface features, at centimeter scale, that could confirm lava flows or similar surface deformation. Looking farther ahead, Venus scientists are keen to see a new generation of balloons or airships to taste the planet's atmosphere. It has been suggested that simple microbial life might exist in the cloud tops, though this is pure speculation. One advanced concept being prepared in the US is for a delta winged aircraft called VAMP (the Venus Atmospheric Maneuverable Platform) to be dropped by an orbiter into the clouds. Once in the atmosphere it would switch to flight phase, spending up to a year maneuvering between the upper and mid cloud layers, gathering data to send back to Earth. During the Venusian day, it would fly in the higher atmosphere, charging its batteries from the sunlight, before dipping to lower regions again at night.

ABOUT THE WRITER
Paul Sutherland is a space journalist, and the author of Where Did Pluto Go? Each month he reports on the latest space research in BBC Sky at Night magazine.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

The Realm of Ghosts

Will Gater dives into the region of Virgo, one of the most extraordinary swaths of the night sky, to reveal the science behind the faint galaxies that reside there.

Image by Douglas S, M104 — Sombrero Galaxy

Cast your eye across the band of sky between the star Spica and the handle of The Big Dipper on a clear spring night and what do you see? Save for few stars there doesn't appear to be much to write home about — at least not to the naked eye.

Yet this great swathe of the celestial sphere is arguably one of the most extraordinary patches of our night sky as it's peppered with hundreds of galaxies. Virgo is swarming with faintly glowing celestial forms; there are delicate spiral wisps, fuzzy ellipticals and even great clusters of galaxies gathering in their multitudes. And though they may be hidden to the naked eye, these spectral, stellar gatherings are of enormous interest to astrophysicists. So come with us as we explore the science of some of the more famous inhabitants of Virgo's ghostly galactic realm.

The Sombrero Galaxy

Virgo is a constellation famed for its huge population of distant celestial smudges, one of which is our first object, Messier 104. M104 actually sits close to the border between Virgo and the more southerly constellation Corvus, approximately 11° from the bright star Spica (Alpha Virginis). M104 is more commonly known as the Sombrero Galaxy and it's not difficult to see how it acquired this name when you look at it through a large telescope or see images of it taken by astrophotographers. Its scientific story is every bit as striking as its visual appearance too.

Perhaps its most obvious feature is the dark swathe across the bright mass of stars that make up its glowing oval shape. The swathe is a silhouetted portion of the galaxy's disc of dust and gas, which is viewed edge on from our line of sight. Hubble Space Telescope images have shown this disc in remarkable detail, revealing intricate structures in the dust lanes there. Infrared observations made with the Spitzer Space Telescope meanwhile have revealed that, unusually, M104's disc sits within another, larger elliptical galaxy, only part of which we see in visible light and which only becomes more fully apparent at longer infrared wavelengths.

Abell 1689

Astronomy is full of mind-bending physics — and there's no shortage of weird and wonderful behavior in and around galaxies. Nowhere is this better demonstrated than when distant galaxies swarm together in vast clusters. Abell 1689 is one such galaxy cluster that astronomers have scrutinized intensely in recent decades. It lies at the heart of Virgo, around 7.5° east of the bright star Porrima (Gamma Virginis). At a distance of over two billion lightyears from us, and extremely faint, this cluster is not one you'll be tracking down through the eyepiece of a modest back-garden telescope. But thanks to the powerful orbiting eye of the Hubble Space Telescope, this faraway galactic gathering has been imaged in spectacular detail revealing a lot more than just the individual glowing members of the cluster itself.

Scan your eyes over Hubble's image of Abell 1689 (right) and you might see what makes the cluster so interesting. Scattered throughout it are thin, hair-like arcs of light. These aren't exotic celestial structures, but highly warped visions of other galaxies that sit far beyond the cluster. These arcs appear because the huge combined mass of the cluster galaxies distorts the space surrounding it, causing it to behave like a lens. Though the quality of the image provided by this gravitational lens might raise eyebrows in amateur telescope-making circles, the lens shares one key trait with the telescope lenses we use: it can reveal distant objects that we might otherwise be unable to see. Indeed in 2008 researchers announced that they'd used Hubble, in conjunction with the Abell 1689's gravitational lens, to observe a distant galaxy in the early Universe, some 700 million years after the Big Bang.

M87

Look at any image of the rich fields of galaxies in and around the constellation of Virgo, and among the stars and galactic swirls that fill your view you'll see numerous bright ovals of light. These are elliptical galaxies and although they may not have the beauty or spectacular star-forming regions of their spiral cousins these often vast stellar swarms are some of the most enigmatic intergalactic inhabitants we know of. Foremost among the ellipticals in this part of the sky is the gargantuan M87. It's truly a giant — a recent study by astronomers at the European Southern Observatory was able to determine the size of the halo of stars around the galaxy: the ring of stars spans about 980,000 lightyears, dwarfing the Milky Way's stellar halo, which measures roughly 640,000 lightyears across.

However, M87's most famous feature is not its size but what lies at its heart: a supermassive black hole. Unlike the Milky Way's central black hole M87's is active. Images of the galaxy show an enormous jet emanating from the black hole; the jet is glowing due to light released by high-energy particles that are racing at tremendous speeds along magnetic field lines within it.

Aside from the jet and some globular clusters, though, the rest of M87 might seem rather bland in visible-light. At other wavelengths, however, a hidden maelstrom of activity in and around the enormous galaxy is revealed. Radio telescopes, for example, have observed huge glowing streams of material associated with the black-hole jet, while X-ray images from the orbiting Chandra observatory show immense swirling clouds of superheated gas within the galaxy. Something to consider the next time you set eyes on that seemingly placid, fuzzy patch in your telescope's eyepiece.

The Virgo Galaxy Cluster

Ask a seasoned stargazer to name one of their favorite spring galaxies to observe and chances are it'll be located in Virgo. The constellation boasts an extraordinary array of galactic treasures, including some of the most famous in the sky. It's perhaps no surprise then that many of the galaxies crowding into this part of the heavens are associated, that is they're all part of an enormous — and in cosmic terms relatively nearby — grouping known as the Virgo Galaxy Cluster. Recent surveys suggest that there are some 1,900 galaxies in this cluster, which sits roughly 56 million lightyears from the Milky Way.

The cluster counts within its number many relatively bright galaxies that are familiar to amateur astronomers — for example M87 as well as M86, M84 and the others that make up the sweeping curve of galaxies known as Markarian's Chain. The heart of the cluster itself lies in the region around 6° west of the star Vindemiatrix (Epsilon Virginis). However, modern studies have shown that there are members of the cluster spread all over this patch of sky, with some in neighboring constellations of Coma Berenices and Leo too.

NGC 4488

Looking out into the cosmos, the distances to even the nearest galaxies can seem immense, and yet spiral galaxies collide frequently. As two galaxies approach, their gravitational interactions cause them to distort each other.

You can get a sense of what happens when spiral galaxies engage this way if you look into the constellation of Virgo — specifically within Markarian's Chain. In the chain are two galaxies — known as The Eyes — that lie roughly 50 million lightyears from us. The pair are catalogued as NGC 4438 and NGC 4435, and deep images of NGC 4438 show a contorted jumble of scattered dust lanes and ribbon-like streams of stars around a brighter, central region. Astronomers think that what we're seeing in NGC 4438 is actually a spiral galaxy that's been disrupted by a violent encounter with the elliptical galaxy M86, which now sits less than 0.5° away on the sky.

The Whirlpool Galaxy

This journey across Virgo's ethereal realm of galaxies has taken us across some 60° of the sky and we end our exploration of this extraordinary region with one of the most beautiful galaxies anywhere on the celestial sphere. M51, otherwise known as the Whirlpool Galaxy, has captivated astronomers for centuries and continues to intrigue both amateurs and professionals today. M51 was being scrutinized by astronomers long before its true nature — as a galaxy in its own right and not just another glowing nebula within the Milky Way — was really known.

William Parsons, the third Earl of Rosse, famously sketched M51 in 1845 using the enormous Leviathan of Parsonstown, a 72-inch reflecting telescope housed at Birr Castle in Ireland. His exquisite drawing clearly depicts the sweeping form of the Whirlpool — and its neighbor, the galaxy NGC 519 that's instantly recognizable in the astro images taken with today's photographic equipment.

Our perspective of M51, looking down on the galaxy's disc, affords us a superb view of the physics unfolding there. Within the disc, density waves have formed spiral arms, which are home to vast numbers of hot, relatively young, blue stars. Photographs of the galaxy reveal another striking feature of these arms: numerous crimson patches of light scattered throughout M51's disc. This feature is one that, just like the hot young stars, is testament to the star formation occurring there. These crimson patches are regions where the radiation of infant and newborn stars is exciting their surrounding maternal nebulae, causing the gas clouds to shine with the characteristic ruby hue of glowing hydrogen.

These dramatic flourishes of star formation aren't the only dynamism on display with the Whirlpool Galaxy either. NGC 5195 is interacting with M51 and long-exposure images of the pair show extensive swathes of stars — known as tidal streams — near the galaxies that have been drawn out during this gravitational dance.

See the Galaxies

Although none of the galaxies we've covered here are visible to the naked eye, several, such as M104 (the Sombrero Galaxy) and M51 (the Whirlpool Galaxy), are fine sights through amateur telescopes. If you've never observed a distant galaxy through a telescope before, you'll soon realize why many astronomers affectionately refer to deep-sky objects as faint fuzzies. It's a description that sums up rather well the view of many galaxies through the eyepiece of a modest amateur telescope: a faint, fuzzy blob. That's not to say there aren't brighter examples that show more structure or interesting features, such as M104's dark bar, though. As with many celestial objects the key to seeing more detail is to get away from light pollution and use a larger aperture telescope. If you don't have one then pay a visit to your local astronomical society observing evening or star party during the galaxy seasons of spring and autumn. These events often provide access to large-aperture instruments.

ABOUT THE WRITER
Will Gater is an astronomy journalist, author and presenter. Follow him on Twitter at @willgater or visit willgater.com

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Treasures of Orion

Paul Money takes us on a tour of the best sights the Hunter has to offer.

Image by Ron Adams, M42 the Great Orion Nebula

Orion holds something for everyone, whether you enjoy the naked-eye splendor of its stars, want to tour it with a pair of binoculars, peer deeper with a modest telescope or delve into its deepest and faintest targets with 10- to 14-inch systems. It is easy to enjoy the view of the Orion Nebula alone, but a host of astronomical treasures awaits those willing to look a little closer. In this article we reveal some of Orion's most striking features and the equipment needed to see them.

Naked Eye

Allow 30-40 minutes for your eyes to adapt to the dark before you start observing.

Betelgeuse (Alpha Orionis)
RA: 05h 55m 10s
Dec.: +07° 24' 25"
We begin with the most famous star in Orion, mag. +0.5 Betelgeuse (Alpha Orionis). An unmistakable bright orange star of spectral class M0, Betelgeuse is often cited as the most likely red supergiant to go supernova any time in the next million years.

Rigel (Beta Orionis)
RA: 05h 14m 32s
Dec.: –08° 12' 06"
On the opposite side of the Belt stars to Betelgeuse is mag. +0.2 Rigel (Beta Orionis). In contrast to Betelgeuse, Rigel is a brilliant blue-white star of spectral class B8. It is technically a little brighter than Betelgeuse despite being designated Beta.

Binoculars

Delights await you whether you have a pair of 7x42s, 10x50s or 15x70s.

Orion's Belt
RA: 05h 36m 12s (Alnilam)
Dec.: –01° 12' 07" (Alnilam)
With 10x50 binoculars you will see a little deeper. The 6° field of view allows a stunning view of the three stars that form Orion's Belt: mag. +1.9 Alnitak (Zeta Orionis), mag. +1.7 Alnilam (Epsilon Orionis) and mag. +2.4 Mintaka (Delta Orionis). All three are B0 spectral class.

Sword of Orion
RA: 05h 35m 16s (Theta Orionis)
Dec.: –05° 23' 23" (Theta Orionis)
For now let's sidestep the Orion Nebula, as the sword also contains the wonderful open cluster NGC 1981 at the top. A group of stars including mag. +4.6 42 Orionis and mag. +5.2 45 Orionis sits north of the Orion Nebula (M42) and the adjacent De Mairan's Nebula (M43), which itself is above mag. +2.8 Hatsya (Iota Orionis).

Meissa (Lambda Orionis)
RA: 05h 35m 8s
Dec.: +09° 56' 03"
Mag. +3.5 Meissa (Lambda Orionis) is found in a neglected group of stars known as Collinder 69 or the Lambda Orionis Association. Meissa makes a triangle with mag. +4.4 Pi1 Orionis and mag +4.1 Pi2 Orionis. Meissa and the cluster it resides in are thought to be 1,100 lightyears away and certainly worth looking at with larger binoculars.

Orion's Shield
RA 04h 49m 50s (Tabit)
Dec.: +06° 57' 40" (Tabit)
Another neglected pattern is that of Orion's Shield, formed by the six stars designated Pi Orionis (mag. +4.6 Pi1, mag. +4.4 Pi2, mag. +3.2 Pi3, mag. +3.7 Pi4, mag. +3.7 Pi5, and mag. +4.5 Pi6). They form a curved line best seen with low-power binoculars, such as a pair of 7x42s, as the distance between the two ends of the shield is 8.5°. Pi3 Orionis, also known as Tabit, is a relatively close 26 lightyears away.

Small Telescope

Use a reflector up to 6 inches or refractor up to 4 inches and you'll see more detail.

The Orion Nebula
RA: 05h 35m 16s (Theta Orionis)
Dec.: –05° 23' 23" (Theta Orionis)
The Orion Nebula is the showpiece of the constellation and really comes alive with a small refractor. It has two patches with Messier designations: M42 is the main nebula, its wisps and tendrils stretching out from the central Trapezium Cluster. Just above it is the much smaller M43, also known as De Mairan's Nebula.

M78
RA: 05h 46m 45s
Dec.: +00° 04' 45"
M78 would be the showcase nebula of the constellation were it not for the Orion Nebula. It possesses two stars immersed in nebulosity, shines at mag. +8.0 and from Earth looks like a typical white-sheeted ghost. Look out for nearby NGC 2071: it is smaller than its neighbor but shines at mag. +8.0.

NGC 2112 and Barnard's Loop
RA: 05h 53m 45s (NGC 2112)
Dec.: +00° 24' 39" (NGC 2112)
The emission nebulosity described as Barnard's Loop is well known among astrophotographers, yet part of its section above and slightly east of M78 can be traced with a 6-inch Dobsonian. This faint, 'milky' patch curves and ends close to mag. +9.0 open cluster NGC 2112. Low magnification is best for the loop.

Sigma Orionis
RA: 05h 38m 44s
Dec.: –02° 36' 00"
Close to mag. +1.9 Alnitak (Zeta Orionis) is mag. +4.0 Sigma Orionis, which appears as a stunning multiple star system through small to medium telescopes. There are four splittable stars, the brightest of which is another double ? though this one is too tight to resolve in amateur instruments.

The Flame Nebula (NGC 2024)
RA: 05h 41m 55s
Dec.: –01° 51' 00"
The Flame Nebula needs dark skies and low magnification to see well. Use a 6-inch reflector, making sure you keep nearby Alnitak out of the field of view to improve contrast, and you should be able to see its mottled fan shape. As a bonus, reflection nebula NGC 2023 lies nearby.

NGC 1662
RA: 04h 48m 27s
Dec.: –02° 56' 38"
Now for something different. NGC 1662 is a lovely mag. +6.4 open cluster forming a right-angle triangle with mag. +4.6 Pi1 Orionis and mag. +4.4 Pi2 Orionis, the two stars at the top of Orion's Shield. Pi1 Orionis sits in the right angle. This is another overlooked target, said to resemble a Klingon Bird of Prey from Star Trek.

NGC 2022
RA: 05h 42m 6s
Dec.: +09° 05' 10"
This little planetary nebula can be found just southeast of mag. +3.5 Meissa (Lambda Orionis). The nebula shines at mag. +11.6. In a 6-inch Dobsonian it is small and round, appearing a pale greenish-blue. It can sustain high magnification if conditions permit.

The 37 Cluster
RA: 06h 08m 24s
Dec.: +13° 57' 53"
Also designated NGC 2169, this cluster gets its name because its stars appear to form the numerals three and seven. A lovely little cluster shining at mag. +5.9 and well worth seeking out even under moderately light-polluted skies. This cluster bears higher magnifications well.

Large Telescope

Delve deep into the constellation with a reflector over 6 inches or a refractor over 4 inches.

The Trapezium Cluster
RA 05h 35m 16s (Theta Orionis)
Dec.: –05° 23' 23" (Theta Orionis)
At the heart of the Orion Nebula is the Trapezium Cluster. The main stars can be easily seen through small scopes, but use a large instrument and two more pop easily into view. Two more challenging stars are mag. +16.0.

Jonckheere 320
RA 05h 05m 40s
Dec.: +10° 42' 21"
This is a stunning but neglected planetary nebula shining at mag. +11.8. In smaller telescopes it looks like a green star at low magnification, so larger telescopes really do it justice and bring out its true nature. Through a 14-inch Newtonian it appears as a small green disc.

NGC 1999
RA: 05h 36m 25s
Dec.: –06° 42' 58"
This is another nebula that could have more attention if it were not for the Orion Nebula. NGC 1999 shines at mag. +9.5 and in small telescopes looks like a small misty star, but a 14-inch scope reveals the mag. +10.3 star V380 Orionis surrounded by faint nebulosity.

NGC 1788
RA: 05h 06m 54s
Dec.: –03° 20' 05"
Off the beaten track and roughly north of mag. +2.8 Cursa (Beta Eridani), NGC 1788 is a reflection nebula that deserves to be better known. It glows by reflecting the light of the mag. +10.0 star embedded within it, and using a large scope reveals more stars around it.

NGC 1924
RA: 05h 28m 02s
Dec.: –05° 18' 39"
Orion is home to dozens of galaxies. One of the easier ones to find is NGC 1924, which lies to the west of M42, shines at mag. +13.3 and may be as far as 100 million lightyears away. When viewed through a 14-inch Newtonian at 200x magnification it appears as a pale, oval smudge of light.

IC 421
RA: 05h 32m 08s
Dec.: –07° 55' 06"
This barred face-on spiral galaxy has a stated magnitude range of mag. +14.2 to mag. +16.4 and is a challenging object. See if you can detect it with a 14-inch Newtonian at 200x magnification as a faint roundish smudge of light. It lies 140 million lightyears away.

UGC 3188
RA: 04h 51m 49s
Dec.: –08° 50' 38"
Use mag. +4.4 Pi2 Orionis to home in on this faint galaxy, which rests just 18 arcminutes east of the star and shines at mag. +15.0. This galaxy has a couple of mag. +10.0 stars nearby that help you locate it. Just south of Pi2 Orionis is UGC 3180, another mag. +15.0 galaxy, this time all alone in the night sky.

The Horsehead Nebula (Barnard 33)
RA 05h 41m 01s
Dec.: –02° 27' 14"
To see the famous Horsehead Nebula, you have to be able to pick up faint emission nebula IC 434, which hangs south from mag +1.9 Alnitak (Zeta Orionis). The horse's head appears as a dark notch through a 14-inch Newtonian and requires averted vision — a great, subtle challenge.

ABOUT THE WRITER
Paul Money is the BBC Sky at Night magazine reviews editor and an experienced astronomer who regularly organizes outreach events.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

The Deep Sky

M42, the Great Orion Nebula, taken by Ron Adams from his backyard in Oakdale, Louisiana.

Galaxies

These concentrations of millions or billions of stars are gravitationally bound together along with gas clouds and pockets of dust. There are probably over 100 billion of them in the Universe. Some of the largest nearby galaxies appear in the night sky as faint smudges of light, but it was only in the early 20th century that astronomer Edwin Hubble proved that they actually exist well beyond our Galaxy — the Milky Way. Before then, they were thought to be spiral-shaped nebulae on its outskirts.

Hubble also established that galaxies vary in shape and size. Two-thirds have distinctive spiral patterns, while the rest range from neat ellipticals to irregular blobs. They can be dwarves containing millions of stars or giants harboring trillions.

Astronomers are still piecing together why this is the case, but collisions and mergers seem to be important in determining how a galaxy evolves. Central black holes also seem to govern how gas is consumed and when stars are formed within these cosmic conurbations.

Galaxies are much more massive than they look. Around 90 percent of their mass is not in luminous stars and gas, but in unseen 'dark matter'. It's arranged in a spherical halo, which governs the motions of the stars within. This invisible cocoon explains why the outskirts of spiral galaxies spin faster than if they were influenced by the quantity of stars and gas alone. Dark matter also governs how galaxies clump together under gravity to form filaments and clusters. Yet dark matter remains an enigma and astronomers are still trying to work out exactly what it is.

Nebulae

These clouds of gas and dust are scattered throughout the Milky Way, mainly in the galactic disc. Nebulae are where stars are created. One idea of how it all starts is that a shockwave from a nearby supernova explosion compresses the cloud. Once the density of the gas passes a critical point, gravity takes over.

Gravity causes clumps of the nebula to pull together. The pressure at the centers of the clumps builds and the temperature rises dramatically. If there is enough gas to fuel the process, the region can become a protostar, an early stage in the making of a star.

If the temperature in the clump reaches 10 million degrees Celsius, the nuclear furnace that powers stars ignites. Over tens of millions of years it settles into normal life and joins what's called the main sequence, like our Sun.

Star Clusters

When you gaze up at the night sky, it looks like a lot of stars are on their own. But a solitary-looking star may be a member of a vast group that's travelling through space as a unit. If we wind the clock back millions of years, we might find these stars forming in the same vast cloud of dust and gas.

Known as open clusters, these families of anywhere from a few dozen to a few thousand stars are created in the dusty spiral arms of the Milky Way. They travel together through space, but gentle tidal forces eventually cause the stars to move apart until they begin to merge into the general starry background.

There is another variety of star cluster out there: the globular cluster. These are much bigger than the open sort, consisting of hundreds of thousands or millions of generally reddish, older stars. Whereas open clusters are found and made within the plane of the Milky Way, globular clusters form a halo around it and their creation is less well understood.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Icy Wanderers

Spectacular comets may be visible only once in a lifetime.

Image courtesy of NASA.

Wandering through the Solar System, comets can be among the most incredible of astronomical sights and, after years of careful observation, astronomers have coaxed out the secrets hidden within their glow.

The heart of a comet is its nucleus, a core of ice laced with rock and dust, a few kilometers wide. Though sometimes called a 'dirty snowball', the ice found on comets is far more exotic than that on Earth.

When the Rosetta spacecraft reached the comet 67P/Churyumov-Gerasimenko in 2014 it performed the first in-situ analysis of the comet's nucleus, finding not only water ice, but also carbon dioxide and monoxide, as well as traces of ammonia, methane and methanol. These highly volatile compounds are usually found as a gas or liquid on Earth, but the frigid depths of space have frozen them to ice as hard as rock.

These snowballs travel in huge elliptical orbits, briefly visiting the inner Solar System at one end before travelling billions of kilometers to the outer regions. 'Long-period comets' travel into deep space, taking thousands of years to complete an orbit, while 'short-period comets' have orbits that take only a few years or decades. Halley's Comet is visible to the naked eye from Earth every 75.3 years.

Comas & Tails

It's thought short-period comets come from the Kuiper Belt, after being knocked out of orbit. Beyond the Kuiper Belt, the Oort Cloud stretches to 3.2 lightyears from the Sun. If a passing star kicks one of its bodies off course, it creates a long-period comet.

For most of these orbits, the nucleus remains an inert lump of ice, but this changes as the comet nears 'perihelion' — its closest approach to the Sun. When close enough, the solar radiation heats the surface, causing the volatile components to boil. As the gas escapes into deep space it lifts off dust, creating a shroud that can stretch out over 50,000km around it — the coma.

As the comet gets closer to the Sun, this envelope begins to feel the solar influence even more acutely, as its wind and magnetic field sweep the dust and gas out into a huge tail, which can extend for millions of kilometers. Some of the tail's debris is left behind in its orbit, forming a meteoroid stream. Several of these cross the Earth's orbit, and when we pass through them every year, we see the debris burning up in the atmosphere as a meteor shower.

Sunlight reflecting off the coma and tail causes these celestial visitors to glow in the night, making them an ever-popular target for astronomers. But, only a handful of comets can be seen every year with the aid of a small telescope. Websites such as www.icq.eps.harvard.edu/cometobs.html or www.ast.cam.ac.uk/~jds will tell you which comets are active and where to find them.

Chasing the Tail

The most alluring part of a comet is surely its huge tail, but it's not always obvious that there are two. The most apparent is the dust tail, swept out in an arc by the solar wind. However, the magnetic field captures the gas, forming a fainter second tail. Sometimes the comet's position relative to Earth means the tails appear to go in two different directions.

Famous Comets

Dominating the sky or the landing site for a probe, these are the best-known comets

Hale-Bopp
Closest approach: 136 million km
Orbit: 2,520-2,533 years
Famed for: Visible to the naked eye for a record 18 months in 1996/97, Hale-Bopp will return around the year 4385.

67P/Churyumov-Gerasimenko
Closest approach: 186 million km
Orbit: 6.4 years
Famed for: Target of the Rosetta mission, which sent the Philae lander to its surface, finding water and organic compounds.

Great Daylight Comet
Closest approach: 19 million km
Orbit: 57,300 years
Famed for: Spotted in January 1910, this comet quickly brightened until it outshone even Venus. Its tail was noticeably curved.

Halley's Comet
Closest approach: 88 million km
Orbit: 75.3 years
Famed for: The only known short-period comet routinely visible to the naked eye, this regular visitor was observed as early as 240 BC.

Ikeya-Seki
Closest approach: 450,000 km
Orbit: 876.7 years
Famed for: Its 1965 close pass of the sun made Ikeya-Seki one of the brightest comets in 1,000 years. It's thought to be a fragment of the Great Comet of 1106.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Starting with Binoculars

Telescopes aren't the only option for observing the night sky, a pair of binoculars is ideal for budding astronomers.

Observing the heavens © Ashley Dace, cc-by-sa.

New to astronomy and trying to work out what to buy for your first telescope? There's a simple answer to that question: don't buy one, buy two. Two small scopes joined with a hinge so that the distance between them can be adjusted to exactly match your eyes — binoculars. Binoculars allow you to observe hundreds of astronomical objects. Not only can you see many more objects through binoculars than with the naked eye, but the detail and color you can see will become richer too.

Binoculars are still suitable even if you want to do 'serious' astronomy. There are variable star observing programs designed specifically for binoculars and being lightweight and easy to carry makes them ideal for getting out and about to view a lunar graze or asteroid occultation.

Closer to home, why not simply wrap up warm, lie back on your garden recliner and just enjoy the objects your binoculars let you find as you cast your gaze among the stars. You'll soon be able to find your way around the night sky and navigate better than with the entry-level GoTo telescope you nearly bought instead.

What Size Should You Buy?

You'll notice that binoculars are classified by two numbers, their magnification and aperture. A 10x50 pair of binoculars has a magnification of 10x and each of the front lenses has an aperture of 50mm. These numbers also allow you to work out the size of the circle of light, or 'exit pupil', that emerges from the eyepieces: to do this you divide the aperture by the magnification. This means a 10x50 pair of binoculars has an exit pupil of 5mm. The exit pupil should be no larger than the dark-dilated pupils of your eyes: so a pupil of anywhere between 4-6mm is fine for your first pair of binoculars. Larger apertures can show you more but being heavier you will probably need to use a mount to keep a steady view over a longer period. The most common sizes are:

1. 8x40: almost anyone over the age of 10 can hold these steadily.


2. 10x50: most adults can hold these steadily, so this size is a popular compromise between size and weight.


3. 15x70: this size really needs to be mounted, although they can be held for short periods.

It's also important to check that the distance between the two eyepieces will adjust to your eyes. If you wear glasses, check that the binoculars have enough distance from the eyepiece to your ideal eye position; 18mm or more should be adequate. Finally, there are two basic types of binoculars: Porro-prism and roof-prism. In any price range, roof-prisms are lighter but Porro-prisms tend to have better optical quality. Once you've decided on the size and type that best suits you, go for the best quality you can buy for your budget.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

The Great American Eclipse

Dan Falk looks forward to the moment when day turns into night across North America.

Image by Luc Viatour, www.Lucnix.be

The date is etched in the brains of eclipse enthusiasts: August 21, 2017. On that Monday, for the first time in nearly 40 years, the path of a total solar eclipse cuts right across the US. For about two and a half minutes, the Moon will completely cover the face of the Sun, turning day into night.

For thousands of years, solar eclipses were seen as shocking, fearful events; our ancestors would witness them and wonder if the world was coming to an end. Today, eclipses no longer take us by surprise: astronomers can calculate when an eclipse will occur hundreds of years in advance. Knowing the physics behind an eclipse, however, doesn't diminish the spectacle. A total solar eclipse is, quite simply, a spellbinding event, one of the most captivating phenomena the natural world has to offer.

People that have never seen a total eclipse might question what all the fuss is about, says astronomer, author and photographer Alan Dyer. "They think it just gets dark, the same way it does every night. No! A total eclipse is unlike anything you've experienced," says Dyer, who's seen 15 total eclipses over the past 40 years. (I've been lucky enough to see four of them, including one that I observed from Easter Island in 2010.) "You see, hear and feel a total solar eclipse," Dyer says. "Experience one and you'll be hooked."

There's another bonus: an eclipse can be enjoyed without any expensive astronomical equipment; you don't need a telescope or even binoculars. A word of caution is in order, though.

During the partial phases of the eclipse, when some portion of the Sun's disc remains visible, it's not safe to look at directly without eclipse glasses or equipment fitted with a certified solar filter. But when the Moon is completely covering the Sun — during the total phase of the eclipse — you can gawk at it safely. You can even use binoculars or take photos with a telephoto lens (again, that's only during totality).

It's been a long wait for the Moon to cast its shadow on US soil again. The last time was in 1991, when it landed in Hawaii but didn't reach the mainland. Prior to that it was 1979, when observers in the contiguous 48 states last saw a total eclipse, and even then it was only visible from the northwestern corner of the country.

Chasing shadows

The situation for eclipse observers will be very different in August. The path of totality — the narrow zone within which the total eclipse will be visible — will be just 110km wide, but will stretch from coast to coast, running from Oregon to South Carolina.

During a solar eclipse, the Moon's shadow (think of it as a very long, narrow cone that points away from the Sun) makes contact with Earth's surface. Since Earth rotates east to west, the Moon's shadow travels along in the opposite direction, running from west to east. After making landfall on Oregon's Pacific coast, the shadow continues east through the Rockies and on into the nation's heartland. It continues its eastward rush, crossing the Appalachian Mountains and finally zipping across the Carolinas and out over the Atlantic, near the historic city of Charleston.

Note that simply being within the path of totality isn't enough: you'll want to be near the middle of the path, known as the centre line. Most locations near the centre line will experience about two and a half minutes of totality. People living just south of Carbondale, Illinois, can brag that they'll get the longest duration of totality, with a little over two minutes and 40 seconds. That duration drops sharply as you move away from the centre line. Meanwhile, anyone viewing from north or south of the path of totality will experience a partial eclipse — far less dramatic than totality.

As the moment of totality approaches, the entire landscape can appear altered. In the half-hour or so before the Sun disappears, the quality of the light changes, shadows get sharper and the temperature drops. Dogs bark and roosters crow in confusion. This is the moment to make sure the batteries in your cameras are fully charged.

Because the eclipse path cuts right through the US, a record number of people are expected to witness the spectacle. More than 10 million Americans live within the path of totality; nearly 30 million live within 100km of the path. Some are already calling on the federal government to declare Monday August 21, 2017 a national holiday.

Location, location, location

With the eclipse's path running some 4,500km across America, where should you go to watch it? The weather, of course, is a big issue. Roughly speaking, the weather prospects improve from east to west; once you're west of the Mississippi, you've got a better than 50/50 chance of having a clear sky on 21 August, based on many years of climate data. Of course, what the local forecast says the day before the eclipse is more important than historical weather data! Some of the driest spots, with the highest chances of clear skies, include the valleys of central Oregon and central Idaho; some locations have a roughly three-in-four chance of cloudless weather. And of course, there's the scenery. No doubt, many visitors will be drawn to places like Grand Teton National Park, in northwest Wyoming, right inside the path of totality. Nearby Yellowstone is just outside the path, but many people will likely drop by for a visit before or afterward.

Another big unknown, apart from the weather, is the size of the crowds. "My guess is that they'll come by the thousands, from all over the US and other parts of the world," says Randy Holst, President of the Boise Astronomical Society in Idaho. Congestion is a real concern: most of the highways in the Northwest, especially those in the mountains, are two-lane, winding roads. And as Holst and others point out, this part of the country is famous for its natural beauty and is often jam-packed with tourists in August, even when there's no eclipse. Not surprisingly, many hotels and campsites are already booked up — but remember, this is an eclipse that you can, at least in theory, drive to; if your hotel is 80km outside the path of totality, you may still be okay — as long as you don't end up stuck in traffic!

Farther east, the population density is greater; millions of Americans will be able to see the eclipse from their backyards. "Every day the momentum is building," says Don Ficken, who heads the Eclipse Task Force for the greater St Louis area, in Missouri. "This is a historic event." In Columbia, Missouri, 50,000 people are expected to gather at a public event at the city's football stadium; the airport in St Joseph, in the northwest of the state, will host up to 60,000 at an eclipse-viewing event. Details for other events, large and small, are likely to be announced in the months ahead.

But what if you miss this particular eclipse? The next total solar eclipse you could go and witness will happen on 2 July 2019 — the path of totality passes through Chile and Argentina. The next one visible from the US comes on 8 April 2024.

Why wait until then, though? As solar eclipses go, this one is relatively accessible and the weather prospects in many locations are reasonably good. As Jay Anderson, a meteorologist and avid eclipse chaser puts it, "You only go around once. So do it while you can."

Top places to view the eclipse

Five of the best locations to see totality from

Grand Teton National Park, Wyoming
The park features some of the most spectacular mountain scenery in the US, and equally majestic Yellowstone, known for its wildlife as well as the Old Faithful geyser, is right next door.

Carbondale, Illinois
If you want the longest possible eclipse, a spot just south of this small university city boasts the maximum duration of totality. Totality is expected to be just over two minutes and 40 seconds here.

Central Nebraska
What's in central Nebraska? A useful 400km stretch of Interstate 80, which happens to run along the path of totality. If may also make an emergency relocation possible if bad weather is forecast on the 21st.

Charleston, South Carolina
Tourists and history buffs flock to this picturesque city on the Atlantic coast even when there's no eclipse. The first shots of the American Civil War rang out over Charleston's harbour on 12 April 1861.

Madras, Oregon
This part of Oregon boasts some of the driest conditions anywhere along the path of totality; statistically, there's about a 65 per cent chance of having a clear sky on Monday 21 August.

Viewing and Imaging the Eclipse

Here's how to get the most out of nature's greatest spectacle

1. Weather forecasts, along with your rental car, may be your best friend. Check the forecast the night before the eclipse and again in the morning. You've come this far, another bit of driving — if it gets you to clearer skies — may be well worth it.


2. Before and after totality, the Sun is far too bright to look at directly — so don't, unless you have a certified solar filter. Your local astronomy club can help you get your hands on one.


3. The partial phases of the eclipse last much longer than the brief moments of totality — so enjoy this slow period. Notice the changing quality of light and shadow as the Sun is reduced to a thin sliver of light.


4. The two and a half minutes of totality will go by very fast. Have a plan for how you want to spend that time. If you want to take photos, be sure that your batteries are fully charged.


5. If you have binoculars, use them during totality. They'll bring out the details in the Sun's pearly-white corona (its tenuous outer atmosphere). They'll also help you see the bright-red solar prominences that flare up from the Sun's surface.


6. During totality, take a few moments to look at the overall scene in the sky. Can you see the bright planet Venus, above and to the right of the hidden Sun?


7. "Pictures or it didn't happen." So the younger generation say. But do you really want to spend those two and a half minutes of totality fiddling with your camera? There's a lot to be said for just looking.


8. If photography is a must, consider taking wide-angle views that include the scenery. Close-up views of the eclipse all look pretty much the same; a wide-angle shot from your location will be more unusual.

ABOUT THE WRITER:
Dan Falk is a science journalist based in Toronto. His books include The Science of Shakespeare and In Search of Time. Find him at @danfalk

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

The Outer Gas Giants

These distant worlds include the Solar System's largest

By NASA (JPL image) [Public domain], via Wikimedia Commons

Jupiter

Diameter: 143,000km

Moons: 67

Distance from Sun: 778 million km

The largest planet in the Solar System, Jupiter has more mass than all of the other planets put together and is second only to the Sun in terms of gravitational power. In 1994 it enticed comet Shoemaker-Levy 9 to fragment and crash into its swirling clouds — other likely comet crashes were recorded in 2009, 2010 and 2016. Jupiter is mostly gas, its composition of hydrogen and helium similar to that of the Sun.

With a good pair of binoculars the first things you'll notice are its four most famous moons: Io, Europa, Ganymede and Callisto, spied by Galileo Galilei in 1610. With a telescope you'll see a slightly squashed sphere. This is due to its fast spinning 'day' of just under 10 hours, which causes the equator to bulge outwards and the poles to flatten. Jupiter's cloudy atmosphere is revealed as dark bands separated by white zones. The longer you look, the more features appear, so keep an eye out for spots, wisps and kinks. The most famous feature is the Great Red Spot; twice the width of Earth, this is a gigantic storm with winds reaching up to 644km/h.

Saturn

Diameter: 120,500km

Moons: 62

Distance from Sun: 1.43 billion km

Saturn is known for its spectacular rings, made from millions of chunks of water-ice spread out into a thin disc only a few tens of meters thick but stretching 100,000km from the planet's surface. The rings form bands, some broad, some narrow. Scores of moons orbit within the rings, some carving out wide gaps. As with Jupiter, a handful of them are visible to observers.

Saturn's brightness varies due to the way the rings are tilted and how much sunlight they reflect. The planet is not so bright when the rings are edge-on to us, but its brightness increases over 7.5 years as the rings open up to observers on Earth. Then it fades again over the same period. If you're wondering why this takes 7.5 years, it's a quarter of the time that Saturn takes to go around the Sun.

The best way of understanding Saturn's tilting effect is to go out and look at the planet — it really is one of the telescopic marvels of the Solar System. It doesn't matter if you have a small scope — the sight of this tiny, ringed world hanging in a large, inky black field of view is magical. The view of larger scopes will start to show detail in the rings and on the planet itself.

Uranus

Diameter: 51,000km

Moons: 27

Distance from Sun: 2.87 billion km

The first planet to be discovered with a telescope, found by William Herschel in 1781. Its blue-green hue comes from the abundance of methane ices in its hydrogen and helium atmosphere, which also contains water and ammonia ices. Like Venus, Uranus spins from east to west, but its axis of rotation is tilted almost 90° from the plane of its orbit, suggesting that it might have been knocked over by a collision. Five rings were discovered in 1977 — in 1986 the Voyager spacecraft identified a further six, and two more were found by the Hubble Space Telescope in 2005, bringing the total to 13.

Visually, Uranus doesn't have much going for it, whether you use your eyes, a pair of binoculars or a telescope. By simply turning your head upwards, you can just about see this gaseous world as a very faint star at the limits of visibility (around mag. +5.6). You won't see much from anywhere with light pollution, however — the sky has to be very black. The view improves a little through a telescope, showing a greenish speck.

Neptune

Diameter: 49,500km

Moons: 13

Distance from Sun: 4.5 billion km

Neptune's composition is similar to that of Uranus, being mainly hydrogen and helium with methane ices, water ices and ammonia ices mixed in. But unlike featureless Uranus, Neptune is wracked by stormy weather, with giant tempests boiling among the clouds. Its winds are the fastest in the Solar System, reaching an incredible 600m/s (that's 2,200 km/h). Neptune has six known rings. They appear to have bright clumps within them, which may be short-lived collections of debris.

At around mag. +8.0 you need at least binoculars to see Neptune. When looked at through a telescope it looks like a 'star' with a hint of blue, but it is not as spectacular as its larger, closer compatriots. If you have a very large scope you can also catch a glimpse of Neptune's largest moon, Triton, which is mag. +13.5.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

The Inner Planets

These worlds are mostly made up of metals or silicate rocks.

Released under Creative Commons CC0 on Pixabay.com.

Mercury

Diameter: 4,880km

Moons: 0

Distance from Sun: 58 million km

The closest planet to the Sun, Mercury is a place of extremes. It is the smallest and densest planet in the Solar System, barely larger than our Moon. It takes 59 Earth days to rotate once and 88 to orbit the Sun, meaning its parched surface experiences temperatures hot enough to melt lead on the sunward side, but is sub-Antarctic on the side in shadow.

This small world is a real challenge to observe for a variety of reasons. It's a fast mover, travelling around the Sun four times more quickly than Earth, so don't expect it to hang about in any part of the sky for very long. Mercury's orbit is a fairly eccentric oval shape, and it's on a bit of a tilt too, which means some times are better for viewing it than others: spring evenings and autumn mornings. If that's not tricky enough, you only have a relatively short observation window on any day you choose to look, as Mercury never strays very far from the Sun.

In spring, start looking 30 minutes after sunset, after which you'll have about another 45 minutes to see it. Autumn gives you a longer view, from about an hour and 45 minutes before sunrise, but that does mean getting up exceedingly early.

Venus

Diameter: 12,100km

Moons: 0

Distance from Sun: 108 million km

Venus is sometimes called 'Earth's evil twin'. It is similar in size and composition to our planet, but a dense carbon dioxide atmosphere and sulfuric acid clouds make its surface a hellish 470°C. The planet spins slowly, in the opposite direction to most planets, and takes about the same time to rotate on its axis (243 Earth days) as it does to travel around the Sun (225 days).

As Venus's orbit is slower than Mercury's, it can be visible for months on end, and sometimes for up to three hours after sunset or before sunrise. When Venus is at its brightest, it becomes the third brightest object in the sky, only beaten by the Moon and the Sun. This is caused by sunlight reflecting off its bright white carbon-dioxide clouds, and has led to Venus being called the 'Evening Star' or 'Morning Star' depending on when it appears. Venus can come very close to Earth, plus it's rather big, meaning that it's a good target for binoculars, through which you can easily see its larger phases.

Mars

Diameter: 6,800km

Moons: 2

Distance from Sun: 228 million km

The Red Planet is the most visited extraterrestrial destination in the Solar System. Dozens of missions have ventured there, and they have explored the Martian landscape in incredible detail. Smaller than Earth but with the same land area, Mars is like a cold, rocky desert, littered with canyons and volcanoes. The planet has polar caps and a thin atmosphere of mostly carbon dioxide. Although dry today, Mars's mineral salts and rock formations suggest that it was wet in the past, and could possibly have harbored life.

Mars differs from Mercury and Venus in that its position in the Solar System — on the other side of Earth — means it can be 'up' from sunset until sunrise. A small telescope can reveal lighter, pale-reddish areas, darker patches and the bright white of the ice caps.

The Dwarf Planets

Diameter range: 975km to 2,330km

A dwarf planet is, according to the International Astronomical Union, a body that orbits the Sun and is not a satellite, spherical in shape due to its own gravity and too small to have cleared its orbit of debris and so claim the title of a fully fledged planet. This classification was agreed after the 2005 discovery of Eris, an icy body in the outer Solar System very similar to Pluto, which was then considered a planet. In the fierce debate that followed Pluto was demoted into the newly created class, which also contains outer Solar System bodies Haumea and Makemake, and Ceres in the Asteroid Belt.

Ceres is the largest, but still comparatively small, so you will need binoculars to find it. Pluto is best seen by taking images of the region of sky it is in over consecutive nights and looking for the faint moving dot.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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The Heart of Darkness

At the core of the Milky Way lies an unseen monster. Elizabeth Pearson investigates how astronomers are trying to glimpse the supermassive black hole at the center of our Galaxy.

By Nick Risinger [Public domain], via Wikimedia Commons

At the centre of the Milky Way lies a dark behemoth. One like it is thought to reside in the core of nearly every major galaxy, a hidden heart no one has ever seen — a supermassive black hole.

This body has the mass of over four million Suns but is crammed into a space that's only 20 times our star's diameter. Its gravitational pull is so strong that even light can't escape, meaning that while its influence is felt throughout the Galaxy, we'll never be able to look directly into the black hole.

We aren't completely blind to its mysteries, however. Though the black hole remains shrouded, it's surrounded by a swirling cloud of material known as an accretion disc. As this disc rotates, friction causes the gas and dust in it to heat and glow brightly. The visible part of this glow is shielded by dust, but enough emissions escape at radio wavelengths to create a bright spot 26,000 lightyears away in the constellation of Sagittarius. This radio source is called Sagittarius A* (Sgr A*).

Although enough radio emissions get through the dust for the black hole to be detected, what we can see still seems rather lacklustre compared to what might be expected from looking at the cores of other galaxies.

"The Milky Way's black hole is known to be very inactive. It's radiating several orders of magnitude less than the Eddington luminosity, the maximum luminosity the black hole could have," says Abhijeet Borkar, from the Czech Academy of Sciences in Prague, who was part of a team that spent four years monitoring SgrA* with the Australia Compact Telescope Array.

"Either most of the energy in the accretion disc isn't emitted as radiation, giving it a low luminosity, or there's no stable accretion disc around the black hole. Instead there's a clumpy, discontinuous disc so there is not enough material falling into the inner parts of the accretion disc to maintain its brightness," says Borkar.

Disquiet in the calm

This does not mean the region is a calm and placid place, however. Despite its quiet background emissions, the material around the black hole regularly flares into brightness.

"We see about four instances of flaring each day, when we observe a six-fold increase in the luminosity of the black hole in infrared and X-rays. At radio and submillimetre wavelengths the luminosity increases by 30 per cent," says Borkar.

The flares typically last one or two hours, depending on the wavelength of light observed. They are also likely to originate from material that orbits around the black hole at speeds so fast that the effects of relativity become apparent.

"It's thought that either the light has been Doppler shifted as it goes around the black hole (creating an increase in luminosity when it's coming towards us) or a blob of material gets caught in the base of a jet and is pushed out. And as it's pushed out it expands," says Borkar.

Similar flares have been seen occurring around many other supermassive black holes, but what causes them remains largely unknown. Our proximity to SgrA* gives astronomers a fantastic view of these strange events: by studying the black hole in our Galaxy, astronomers can learn much about these beasts that lie at the centre of every galaxy.

"Black holes are highly significant astronomically," says Frank Eisenhauer from the Max Planck Institute for Extraterrestrial Physics. "They influence the full motion of a galaxy much more than stars do. There is a very strong correlation between the size of black holes and the inner parts of galaxies. They can blow the outer dust about and prevent further gas streaming in, so there's a very strong interplay between the formation and evolution of black holes and the centres of galaxies."

Eisenhauer is the principal investigator for the new Gravity instrument on the VLT, which has been specially made to take advantage of our excellent view of SgrA*. Gravity will image the region around the black hole, not only with an increased resolution compared to previous instruments, but also with a higher precision too. This will allow it to look at the stars that lie around the black hole, which are known as S stars.

"These are stars in the centre of our Galaxy that are a few million years old, with masses around 20 times that of our Sun. They trace the gravitational field and are very good test particles because they are frictionless through the vacuum of space," says Eisenhauer.

The motions of the stars are governed by the black hole they surround. It is by monitoring the motions of these stars that scientists have been able to determine the mass and size of SgrA*. The closer the star, the more accurate the estimation, and the VLT's Gravity instrument will help to refine those measurements.

"Gravity will see fainter stars further in, which are on shorter orbits. We hope to find stars that orbit on the order of a few months or years," says Eisenhauer. Currently the closest known star is S2, which takes 15.5 years to complete one lap around SgrA*. In 2018, it will pass through the point of closest approach — a 'mere' 120 AU from the black hole. During this time, it will be accelerated to 30 million km/h, or 2.5 per cent the speed of light. Travelling this fast means S2 will experience the effects of relativity on its motion, giving the Gravity team a fantastic opportunity to put Einstein's equations through one of their most extreme tests yet.

Little kicks

"Most of the time the star follows Newton's laws, but when it comes very close in 2018 it gets a little kick, and the orientation of its orbital ellipse rotates a bit due to the effects of general relativity," says Eisenhauer. "We know so little about black holes, but they are such a fundamental cornerstone for the understanding of relativity and gravity."

These observations will test Einstein's theories in the one place where they might falter — at the edge of a black hole. "Relativity has passed every test so far, but it hasn't been tested in a scenario where gravity becomes dominant," says Sheperd Doeleman, an astrophysicist from the Smithsonian Astrophysical Observatory. "Gravity is really the weakest force, so it's only near a black hole that it can play with the big boys."

Doeleman is the director of one of the most ambitious astronomical collaborations ever undertaken, the Event Horizon Telescope, which aims to take the first ever image of the shadow cast by the Milky Way's black hole.

"We can't see the black hole directly because it is surrounded by this event horizon that does not permit information to leave the black hole. Because the gravity around the black hole warps light around it, we expect to see the silhouette of the black hole against the backdrop of superheated gas," says Doeleman. "We expect to see a very characteristic strong lensing feature, a ring of light that indicates the last orbit that photons can move through around the black hole before they themselves are sucked in. You end up with an annulus with a relatively dim interior — the silhouette of a black hole."

The size and shape of this silhouette was predicted by Einstein's theories of relativity, which were laid down over 100 years ago. Comparing the shadow that has been forecast with reality could help to solidify our understanding of them. On the other hand, if the observations do not show what is expected, they could throw Einstein's theories into doubt. Within the next year, humankind should have its best look at the dark heart of a galaxy, and with it may even find the key to unlocking the rules that govern our Universe.

Tuning in to a black hole

The center of the Milky Way only became apparent in the age of radio astronomy

In the 1950s, radio astronomy was beginning to come into its own as huge telescopes were built across the world. As radio astronomers surveyed the sky at these newly available wavelengths, a bright new source was discovered in the night sky.

Located at a declination of –29°, the object was best viewed from the southern hemisphere. At the time, one of the largest radio telescopes in the world was the 21.9m 'Hole-in-the-Ground' scope at Dover Heights in Australia, perfectly located to observe this intriguing object. In 1951, the observations of the source, now called Sagittarius A, revealed that it was located at the middle of our Galaxy. In 1958 the International Astronomical Union decided to adopt its position as the centre of the Milky Way.

As radio telescopes increased in size and precision, it became apparent that Sagittarius A was not one single object but something made up of several regions. The eastern section appears to be the remnant of a supernova, while the western part seems to be a three-armed cloud of gas and dust.

In 1974 observations with the National Radio Astronomy Observatory in New Mexico revealed that there was a single bright source embedded within the region, Sagittarius A*. The stars in orbit around it showed the object must have a colossal mass in a tiny area, for which there was only one explanation. The astronomers had found the supermassive black hole at the centre of the Milky Way.

The Event Horizon Telescope

Capturing the heart of our Galaxy requires a telescope the size of the planet

The Event Horizon Telescope (EHT) is one of the biggest projects in the history of astronomy. It aims to combine up to a dozen of the world's premier radio telescopes — from the US, South America, Europe and the south pole — to observe SgrA* in greater detail than ever before.

The telescope works using a technique called very-long baseline interferometry, in which a signal is collected at a number of telescopes. The size of the telescope is not based on the diameter of the dishes, but the distance between them. Each of the scopes has been updated with an atomic clock, the most precise timekeepers on Earth. As well as allowing researchers to make precise timing measurements of the black hole's changing brightness (effectively taking its pulse), the timepieces will make it possible to combine the signals. Using the slight differences in arrival time for the light at each of the scopes, it's possible to reach a much higher precision than can be attained by simply stacking the images together, creating a 'virtual telescope' with the diameter of the Earth.

This huge size is needed as SgrA* is expected to cover a tiny area of sky: around 10 microarcseconds across ? the equivalent of looking for a coin on the surface of the Moon. As the smallest angle resolvable is determined by dividing the wavelength of light by the size of the dish, to further boost the angular resolution of the scope researchers will be observing at 1.3mm. This is the shortest wavelength ever used for the technique and will create an even higher resolution scope.

The EHT's first set of observations will be made on 5-14 April 2017. Once they are completed, the data will be transported to the Massachusetts Institute of Technology, where it will take a supercomputer several months to mix the separate signals into one image. By the beginning of 2018, we should have our first real glimpse of our Galaxy's core.

The Event Horizon Scopes

APEX: Atacama Pathfinder Experiment

ASTE: Atacama Submillimeter Telescope Experiment

ALMA: Atacama Large Millimeter/Submillimeter Array

CARMA: Combined Array for Research in Millimeter-wave Astronomy

CSO: Caltech Submillimeter Observatory

IRAM: Institut de Radioastronomie Millimétrique

JCMT: James Clerk Maxwell Telescope

LMT: Large Millimeter Telescope

MIT: Massachusetts Institute of Technology

NOEMA: Northern Extended Millimeter Array

SMA: Submillimeter Array

SMT: Submillimeter Telescope

SPT: South Pole Telescope

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Buying Your First Telescope

Astronomer Will Gater offers tips and advice on the exciting moment you decide to take the plunge and invest in a telescope.

Image Credit: El Camino College Astronomy Department

One of the things all of us at BBC Sky at Night Magazine love the most about astronomy is that you don't need any fancy or expensive equipment to get started. A warm coat, clear skies and a sense of intrigue about what's up there are all you need to begin your adventure in this wonderful hobby.

But there comes a time, naturally, when your thoughts turn to delving deeper into the heavens and when that happens most people start to think about getting a telescope. If you're at that point now, this article will help to guide you through the process of selecting your first telescope, from the things to look for in an instrument, its mount and the essential, and non-essential, accessories.

What about Binoculars?

The best way to begin is not by diving into the world of apertures and eyepieces, but by taking a step back and asking a question. For the purposes of this guide we're going to assume that you're familiar with the naked-eye night sky and can identify many of the bright stars and constellations, but have never used a telescope before. That's important, because the question, which has become something of a cliché in astronomy circles, is: have you considered getting a decent pair of binoculars first?

There are very good reasons why this question is repeated so often that is become a cliché. First, binoculars can open up a great many more objects to observation than the naked eye, from rich Milky Way star fields to star clusters and the brighter galaxies and nebulae. What's more, a good pair of binoculars will often outperform a cheap, poor-quality starter telescope. But the other reason — and one of the key arguments for considering binoculars before a telescope — is that they offer an easy way to learn crucial observing skills that will be useful later in your astronomy career. For example, with binoculars the experience of moving from a naked-eye view to one seen through an eyepiece is easier, as is learning the essential skill of 'hopping' from one star to another, in a magnified view, to track down a celestial target.

You may have already been using binoculars for a while, though, or perhaps you simply want to jump straight to a telescope. In which case there are some other questions to answer before you begin choosing an instrument. Questions such as what type of telescope do you want; what you intend to do with it; and, of course, how much you're willing to spend. Don't worry if you can't answer these straightaway as there are ways to gather the information you need to make an informed decision for each of them. For example, you could visit your local astronomical society, star party or astronomy trade show before you set foot in a shop. At a society meeting you may be able to see some small telescopes in use and speak to people who have used specific models. At a star party, however, you might even get to look through the telescopes, perhaps even the model you're considering.

What will become immediately obvious when you go to any of these events is the huge array of telescope designs, sizes and mountings that are available. So it's well worth getting to know the different types of telescopes and how to decipher the specifications you may encounter.

Types of Telescopes

Generally speaking, telescopes fall into one of three categories. Firstly, there are reflectors, whose defining feature is an arrangement of mirrors that collect and focus light; then there's refractors, which use glass lenses to do the same things; and finally there are catadioptrics, the telescopes that use a combination of lenses and mirrors to do the job. Within these categories there are numerous permutations and, of course, designs that vary from one manufacturer to another.

Refractors tend to be what most people imagine when they think of a telescope: a lens, or group of lenses, mounted in a long metal tube with the eyepiece (the bit you look through) at the bottom end. Refractors often come with a 'diagonal', an accessory that reflects the view 90° up off the telescope's axis to make your observing easier.

The two most common catadioptric designs are the Maksutov-Cassegrain and the Schmidt-Cassegrain. A Maksutov-Cassegrain telescope uses a curved lens and mirrors mounted in a relatively short, stubby tube while a Schmidt-Cassegrain has a large, glass corrector plate holding a small secondary mirror at one end with the primary mirror mounted at the other end.

When it comes to reflector telescopes, many beginners gravitate towards Newtonian models. In telescopes of this design light is collected by a main mirror housed at the bottom of a long tube. Once it hits this primary mirror the light is reflected back to a smaller secondary mirror that bounces it out at a right angle through the eyepiece. For this reason you look through a Newtonian by standing by the top end of the telescope, rather than the bottom end, and peering through an eyepiece that's mounted on the side of the tube.

The Newtonian design uses the same optical configuration as the other popular type of reflector, the Dobsonian. The difference with a Dobsonian is that the telescope's tube is mounted on a simple rotating base and not the more complex type of mount that Newtonians are typically found on? Which brings us onto the matter of mounts.

Mount up

If a telescope's lens is its eyes, then the mount is its neck. When you look at something, you use your neck to tilt your head up or down and turn it left or right to point your eyes in the right direction. Telescope mounts do exactly the same — they allow the telescope to be moved up and down and turned to the left or right. Astronomers call that upward or downward tilt altitude, and left or right rotation azimuth. So, for instance, Dobsonians sit on a basic altitude-azimuth (more commonly known as altaz) mount, while many Maksutov-Cassegrain and Schmidt-Cassegrain telescopes are attached to one or two computer-controlled arms that are essentially just advanced versions of an altaz mount.

With an altaz mount you need to adjust both the altitude and azimuth settings in order to track an object across the sky and keep it in view. This is because Earth's rotation makes it appear as if the sky is moving, so frequent manual adjustments are required to keep your target centred. That is unless you have an advanced (often expensive) motorised and computer-controlled altaz mount that will take care of the adjustments for you.

But there's another type of mount that gets around this issue in a simple way. The equatorial, or EQ, mount also moves on two axes, but instead of having altitude and azimuth axes, equatorial mounts have a right ascension (RA or polar) axis and a declination axis. These two axes refer to an astronomical coordinate system for navigating the sky that's similar to the latitude and longitude system that's used for navigating on Earth. An equatorial mount is built in such a way that when the RA axis is aligned with Earth's rotational axis, changes need only be made to that one axis to match the sky's movement.

To align an equatorial mount to Earth's rotational axis, the mount's RA axis needs to be pointing precisely towards the north celestial pole — the same point in the sky that Earth's rotational axis points towards. In the northern hemisphere this point is very close to the star Polaris. It's for this reason that many mid-range equatorial mounts come with a small 'polar scope' within the RA axis that has a reticle (targeting crosshair) for precise polar alignment.

Manual or automatic?
Whatever type of mount you end up with it has to be rock-solid. If there's any instability in the tripod's legs or play in the mount's fixings and controls then you'll find observing can become a frustrating affair — another reason to try any telescope before you buy.

While you can track the moving sky manually, it's far more efficient to use an electronically driven mount. These come in several forms from simple, motor-driven equatorial mounts, all the way up to Go-To mounts that, with the aid of a small computer handset (and sometimes GPS), take care of all tracking. Go-To mounts allow you to point your telescope towards a target simply by typing in the object's name or New General Catalogue (NGC) number.

Modern Go-To systems are a superb tool for observing but can often add a lot of money to the price tag of a beginner telescope; money that might be better spent on larger optics sitting on a simpler mount. After all, it's the telescope's aperture — the size of its main mirror or lens — that is perhaps the most important specification. The larger the aperture, the more light can be gathered. Hence most beginners are usually better off going for a good reflector, such as a Newtonian, since refractor telescopes tend to be more expensive than reflectors of the same aperture.

Eyepieces and Finderscopes
After the telescope's main body and the mount, the other key component of any stargazing setup is the eyepiece. The eyepiece is the glass lens that you look through to see whichever celestial body you're observing.

On the side of the eyepiece you'll find a measurement given in millimetres. This is the focal length of the eyepiece and it's by using eyepieces with different focal lengths that you change the magnification of the view through the telescope. The longer the focal length of the eyepiece, the less magnified the view through it will be. It's a good idea to have one or two good-quality eyepieces — one with a short focal length, perhaps around 10mm, and another maybe in the region of 25-30mm — rather than a whole range of cheap ones. And you can completely ignore any marketing hype boasting that a scope can provide hundreds of times magnification — this isn't the measure of a good instrument or a guarantee of superior views. A poor-quality telescope can still magnify many hundreds of times.

Finally, on top of the telescope you'll often find a miniature, low-magnification refractor telescope. This is a finderscope and it's used for centering a celestial object in the main scope's eyepiece. Finder scopes — or their cousins the illuminated red dot/reticule finders — are extremely useful when it comes to tracking down celestial targets.

Needless to say, there's certainly a lot to consider when you buy a telescope. But, then again, a good first telescope will last you many years and be a joy to observe with throughout that time. Choose wisely and your scope will take you on a thrilling journey of discovery that no other pastime can offer.

Which Telescope is best for you?

Answering these questions should help you choose the right first telescope for your needs

What do you want to look at?
Sounds obvious right? The night sky! If you're keen to focus primarily on observing faint galaxies, clusters and nebulae, then it makes sense to go for something like a Dobsonian with as big a mirror as you can afford. A smaller aperture Newtonian on a fancier mount will be more suited to closer, brighter objects.

Which telescope has the right size, weight, portability for you?
A good large-aperture Dobsonian will provide superb views but it may hardly ever be used if you've got to lug it downstairs to observe with. Trade shows are useful for examining many different telescopes in detail to gauge their true size, portability and, to some extent, their build quality.

Is the telescope right for your future aims?
It's worth considering early on where you think your interests may develop in the future. If you think you might eventually want to do more imaging, for example, you may want to choose a telescope with a mount that you can easily upgrade to a more advanced model at a later stage.

Do you need 'feature X' when you could get a better 'feature Y'?
The allure of electronic gadgetry or a computerized mount can be strong when buying your first telescope, but do you really need all that extra tech? You may find that your budget would go much further on a simpler setup with larger optics that'll probably give you better views.

ABOUT THE WRITER
Will Gater is an astronomy journalist and presenter. Follow him on Twitter at @willgater.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

How to Use a Planisphere

When you need to find your bearings in the night sky a planisphere is indispensable, even in our digital age.

This hand colored celestial map of the Stars and Constellations is a steel plate engraving, dating to 1878 by the well regarded French cartographer Migeon. By http://www.geographicus.com/mm5/cartographers/migeon.txt [Public domain], via Wikimedia Commons

They don't look like much — usually a planisphere is simply two discs of cardboard or plastic fastened together with a central pin — but as a new stargazer, you'll soon discover that this tool is one of the greatest aids to helping you navigate the night sky. In fact, this deceptively simple design will allow you to work out which bright stars are in the night sky on any date and at any time throughout the year.

Although the two discs are pinned together, they can still be rotated independently of each other. Printed over most of the lower disc are the stars, constellations and brighter deep-sky objects that you can see from a given latitude. Marked around the outside of this lower disc are the days and months.

Latitude Matters

The upper disc will be slightly smaller than the lower one or will have a clear rim, so you can still see the day and month markings underneath. It also has an oval window in it, revealing part of the star chart on the lower disc. The edge of this window represents the horizon with appropriate north, south, east and west markings and everything within it is the visible sky. Just like the lower disc, the upper disc has markings around its edge. In this case, they indicate the time of day. By lining up the date and time, the stars visible in the window will match the ones in the night sky at that time.

The crucial point to keep in mind when using a planisphere is that they are designed to work at specific latitudes. If you try using one too far north or south of the location it has been intended for, you'll find that the stars don't appear in the right positions.

Getting Started

Follow these simple steps and you'll soon be navigating the night sky like a pro

1. Find Your Bearings
   Before you can start using your planisphere you need to know the cardinal points from where you live. If you don't have a compass, use the Sun. It rises roughly in the east and sets roughly in the west. You can also download a free compass app for most smartphones.


2. Set the Time and Date
   Let's imagine that you are heading out to observe at 9pm on October 15th. Spin the upper disc to align the 9pm marker on this disc with the October 15th marker on the lower disc. The stars in the oval window should now match the stars in the night sky above you.


3. Look to the North
   Look north to begin with, holding the planisphere up so that the word 'north' is at the bottom. If you change the direction you're facing, you need to move the planisphere round so that the compass point sitting at the bottom corresponds with the direction you're facing.


4. Start at the Big Dipper
   Helpfully, the central pin in your planisphere represents Polaris and the north celestial pole. Just to its lower right will be the seven bright stars of the Big Dipper asterism. Use the Big Dipper and the five stars forming the distinct 'W' shape of Cassiopeia to get to know the constellations.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

A Time of Tumult

Elizabeth Pearson investigates how the Solar System was transformed 3.9 billion years ago.

This digital collage contains a highly stylized rendition of our solar system and points beyond. Image Credit: NASA/JPL

When the Solar System first formed 4.5 billion years ago it was a violent place. But quickly, by 4.4 billion years or so ago, the planets had calmed into a familiar configuration — several rocky inner worlds surrounded by gas giants ringed by icy objects. Then, four billion years ago, something catastrophic happened. The planets were thrown once more into chaos, and the face of the Solar System changed forever. This period of upheaval reveals startling truths about the evolution of our home planetary system, and perhaps the origins of life itself.

In the Solar System's first hundred million years or so, the beginnings of planets clumped together from the dust of a boiling protoplanetary disc around our young star. Frequently the young planets would collide and grow larger, though sometimes they would be destroyed entirely. To start, this early Solar System was much like it is today, but there were several key differences.

"Today, we have giant planets from Jupiter at about 5 AU from the Sun to Neptune at about 30 AU," says William Bottke from the Southwest Research Institute in Boulder, Colorado; 1 AU is the distance between the Earth and the Sun. "Modelling work shows the ice giants Neptune and Uranus would never have reached their current sizes if they had to form in the current configuration of the planets. Studies suggested instead that all these bodies formed between about 5 and 20 AU. Beyond that lies the Kuiper Belt. What's interesting about the Kuiper Belt now is that a lot of objects have very special orbits, called resonances. It's very hard to get them into these resonances."

Synced Surprise

A resonant orbit occurs when the ratio between the orbits of two bodies is two whole numbers. Pluto and Neptune share a resonance: for every two orbits Pluto makes, Neptune completes three. To explain what might have caused these resonances, as well as the change in the ice giants' positions, a group of researchers in Nice, France, came up with what is now known as the Nice model in 2005.

"They suggested that you had a gigantic Kuiper Belt with maybe 10 Earth masses in it," says Bottke. "This lets you form Neptune and Uranus on reasonable timescales and you can make lots of Pluto-like objects in the primordial disc."

Using this setup, the team created a computer model of the early Solar System. It's thought that a few hundred years after the formation of Jupiter, leftover gas dragged on the planet and caused it to drift deeper into the Solar System. In time this caused the giant planets to fall into a resonance and their combined gravity acted on the surrounding Kuiper Belt objects, pulling them inwards. In turn, these bodies pulled on the orbits of the gas giants. Though only a small effect compared to that of the planets, little by little the icy rocks began to upset the precarious gravitational balance.

"They found that when the system becomes unstable, Uranus and Neptune move into the primordial disc and actually migrate across it. The giant planets end up with almost identical orbits to what we see today," says Bottke.

This would have thrown the Solar System into disarray. According to the model, Jupiter moved inward while the other gas giants moved out. In turn, the inner planets were jostled and shuffled, pulling some of them into highly eccentric orbits which might have flung some of our siblings out into the Galaxy.

"There's pretty compelling evidence that we didn't start with four giant planets, but five. We had an extra Neptune and then lost it in this process. Jupiter is so massive that anything that encounters it has a good chance of being thrown out of the Solar System," says Bottke.

The addition of a fifth planet to the Nice model also helps to explain observations of the small bodies around Jupiter, as well as certain aspects of the asteroid belt. Could it be that our long-lost sibling is currently floating between the distant stars?

Mass Migration

But planets are not the only things that the Nice model predicts being relocated during this time. The Kuiper Belt currently contains around the same mass as Mars, meaning that during this planetary reshuffle, 99 percent of its mass would have been redistributed. Many Kuiper Belt bodies have been sent hurtling towards the inner Solar System. And it's the scars left behind by these impacts that could help explain a lunar mystery that has been around since the first moonrock samples were brought back by the Apollo missions.

"Many of the Apollo samples, more than you would expect, had been melted in impacts that took place around 3.9 billion years ago," says Barbara Cohen, a planetary scientist at NASA's Marshall Space Flight Center. "You would think that there would be a lot of impact craters from when the Moon formed 4.5 billion years ago, which would fall off as the impactors got used up, but we didn't see any. Instead we saw a lot at 3.9 billion years ago, which was a strange and unusual result."

Apollo scientists hypothesized that 3.9 billion years ago the inner Solar System was pelted with comet-like objects at an impact rate 100 times larger than what's seen today — an era now known as the late heavy bombardment (LHB). However, all the Apollo samples came from a limited area of the Moon, close to the large Imbrium Basin. This 1,150km-wide crater is the result of a huge impact 3.85-3.9 billion years ago, which then flooded with lava. While this is one of the largest examples of the effect the LHB had on the lunar landscape, there is also the chance that all the Apollo samples were simply the ejecta of this one event. To create a bigger picture Cohen had to look towards our only other samples from the Moon — lunar meteorites.

"The meteorites I've been looking at are from places that the astronauts didn't go, they have different geochemical signatures so we think they are from faraway places," she says. "I didn't find any of them to be very old. We see a big pile up at 3.9 billion years, with a long tail off. This tells us there was a prolonged impact rate on the Moon, and then over time the impacts got smaller and smaller."

The Same Old Story

Other meteorites from the asteroid Vesta tell much the same story, indicating a lack of impacts between four and 4.5 billion years ago. But relying on meteorites means that researchers investigating the bombardment history of the Solar System are constrained, as they can only study what happens to arrive on Earth. It's currently impossible to identify meteorites from Mercury and Venus, and all known Martian rocks are volcanic in origin. This leaves large holes in the impact timeline, ones that are unlikely to be filled until we can test the craters directly. Luckily that day could come relatively soon.

"I'm developing an instrument that we could take to Mars to find impact craters and get geochronology on them," says Cohen. "It would have a precision of around 100 million years, a few per cent the age of the crater. That's good enough to distinguish major geologic events in the planet's history."

The recent renaissance in lunar missions means we could soon understand the Moon's history a little better. China's Chang'e program aims to return the first sample from the Moon in over 40 years in late 2017, and then to land the first ever probe on the far side of the Moon in 2019.

A full impact history will prove useful in solving one of the main debates around the LHB. "The question is whether the LHB was a unique event," says Herbert Frey, chief of NASA Goddard Space Flight Center's planetary geology, geophysics and geochemistry lab. "Astronomers have always been keen to know if this is an impact rate spike or whether it is the tail end of a bombardment that had been going on for a long time and we're just seeing the ones that managed to survive because they came in last."

Understanding the precise timing of the bombardment is key to those considering the Nice model. The length of the delay between the Solar System's formation and the bombardment is central to working out what our Universe looked like before the migration.

Though there are still many mysteries surrounding this era this one is certain — our Solar System became a very different place four billion years ago.

The Lasting Effect

The effects of the bombardment can be seen in more than just the craters left behind

Titan

Saturn's largest moon, Titan, is now covered in a thick nitrogen atmosphere but it's unclear when this was created — during the moon's formation or at a later date. If it formed with the moon, then it must have been much thicker as the bombardment would have blasted much of the gas away. Alternately, it could be that the bombardment provided the energy needed to liberate the gas from ammonia ice on the moon's surface.

Mercury

The Caloris Basin, the largest impact basin on Mercury, was formed during the late heavy bombardment. The collision that created the 1,550km-wide site is thought to have been strong enough that it sent shockwaves through the entire planet, creating an undulating terrain on Mercury's other side. It's also been supposed that the impact could have kickstarted volcanic activity on the planet, which created its smooth plains.

Ganymede

Despite being similar in size and composition, Jovian moon Ganymede is very different from its sister, Callisto. While the former has a tectonically evolved surface and a differentiated core, the latter does not. One explanation is that a giant impact struck Ganymede, but not Callisto. The energy from this collision enhanced geologic processes, causing a fully separated iron core and subsurface ocean to form.

Mars

Bombardment would have melted Mars's subsurface ice and produced enough heat to create a temporary climate that might have had the right conditions for life to start. Unfortunately, such conditions would have only lasted a few million years, before the constant shelling began to erode away more atmosphere than it created. By the end of the era, Mars was the cold and dry planet that we recognize today.

The Bombardment of Earth

Despite the extreme conditions of the bombardment, could life have survived the LHB?

On Earth the end of the late heavy bombardment (LHB) coincides with another important epoch for our planet — the emergence of life.

When the LHB was first postulated it was thought that comet-like impactors may have brought the ingredients necessary for life, most notably water. However, findings from missions such as Rosetta show that it's unlikely comets brought any appreciable about of water to the Earth, though they may have brought other prebiotic compounds such as hydrocarbons.

Another theory is that life emerged long before the bombardment, but that all evidence was eradicated by the barrage. If this was so, then only the hardiest of life would have survived. An impact large enough to affect the global environment would have struck every century or so. And around every 10 million years there would have been an impact large enough to melt up to 10 per cent of the surface.

But even such colossal collisions would not have destroyed all havens for life across the planet. While the top few kilometers of ocean might boil away, there could still be enough water left behind for life to survive.

"It's quite possible that life started before, and found ways to protect itself," says Herbert Frey of NASA's Goddard Space Flight Center. "I think life is pretty hardy once it gets started, and it may have found a way to survive through that."

ABOUT THE WRITER
Dr Elizabeth Pearson is BBC Sky at Night Magazine's news editor. She gained her PhD in extragalactic astronomy at Cardiff University.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Cassini the Ring Grazer

As the Cassini spacecraft prepares to fly between Saturn and its rings, Will Gater looks at the latest results from the mission.

Image Credit: NASA

As most of us were getting up to go to work on 16 January this year, NASA's Cassini spacecraft was making a spectacular dive towards the rings of Saturn, some 1.6 billion km away. From high above the planet's pastel-yellow globe, Cassini's trajectory brought it racing down past the outer edge of the planet's main rings, in what the mission team are calling a 'ring-grazing' orbit. These thrilling close swoops, which draw to a close in April, in some ways mark the penultimate phase of Cassini's time at Saturn — a paradigm-shifting exploration that began over a decade ago and which will end in September this year when the spacecraft will be crashed into the gas giant's atmosphere. But the ring-grazing orbits are also evidence of how the Cassini team intends to squeeze every last drop of science from the veteran spacecraft, all the while capturing imagery of breathtaking detail.

One such image, of the tiny moon Daphnis, was captured by Cassini's cameras during the probe's close pass of the rings on 16 January. Daphnis is just 8km wide and looks, like many small moons throughout the Solar System do, like a pockmarked potato. Unlike Saturn's larger moons — Titan, Rhea and Dione, for example — it actually orbits within the planet's main rings, close to the outer periphery of the so-called A ring. And its presence there profoundly influences its surroundings.

Daphnis's most obvious impact on the rings is a thin parting that it has created in the icy material. The 'Keeler Gap', as it's known, spans a mere 42km and extends all the way around the A ring. But to see Daphnis's most striking creations one needs to look a little closer to the moon itself.

Either side of Daphnis, on the diagonally opposing edges of the Keeler Gap, the ring material has been swept into exquisite wave-like structures. Cassini's scientists have been scrutinising these extraordinary features from afar for years, but the spacecraft's ring-grazing orbit on 16 January afforded them their finest — and closest — sighting of the mission so far.

Many rings, one disc

To understand what's going on in the new image we first need to briefly explore the physics of the rings themselves — a system that is composed of countless individual objects. "The particles in Saturn's rings range from marble-sized to house size," says Matthew Tiscareno, a Cassini scientist based at the SETI Institute in California, US.

And while the major sections of Saturn's famous ring system certainly have their own designations — the 'A ring', the 'B ring' and so on — it's best not to think of them as a collection of rings.

"This is one of my pet peeves. It's a very common misconception," explains Tiscareno. "There are very few gaps that would separate one ring from another. Instead you should think of it more as a broad disc. But each part of the disc is orbiting Saturn at a different rate."

This motion plays an important role in the creation of the Daphnis wave structures seen in Cassini's recent image. In fact, researchers use modified equations relating to fluids to examine the physics of Saturn's rings, says Jeff Cuzzi, a Cassini scientist and ring expert at NASA's Ames Research Center in California. "[At] the top of the image the ring particles are moving towards the right the fastest. Daphnis is going a little slower. And then the material at the bottom is going the slowest," he says. "You can think of this material at the bottom as flowing past Daphnis from right to left".

It's when the ring particles drift by Daphnis that the gravity of the small moon leaves its mark. "As it goes by, it experiences a gravitational pull towards Daphnis," explains Cuzzi. "That distorts the orbits [of the ring particles] pulling them up towards Daphnis."

The end result is a series of beautiful wave-like peaks trailing the moon, two of which are seen in remarkable detail in the Cassini image shown left. Multiple waves are created — and there are even more out of shot — because, as Daphnis goes around Saturn, the slower orbiting material it has disrupted at the outer edge of the Keeler Gap lags behind the moon in its orbit; Daphnis thus has a constant stream of unperturbed edge material parading past it that it can repeat the 'rippling' process on. "So in that second wave to the left of Daphnis [are] the particles that had encountered Daphnis, just like in that first wave one orbit ago," says Cuzzi.

Daphnis's gravity also creates waves on the inner edge of the Keeler Gap. But, because the material there is orbiting faster than the moon, the waves extend in the opposite direction to those on the outer edge. In the same image you can see that, to the right of Daphnis, the ring particles on the inner edge have been subtly deflected. This is the onset of one of the inner-edge waves.

Cuzzi says there's an Earthly analogy for this remarkable interaction between Daphnis and the edge of the Keeler Gap. "Think about a river going by and there's a rock in the river. As the river goes by the rock, the water flows up and down and you get this ripple downstream of the rock. This is exactly what we're seeing here," he explains. "In the river the ripple is always fixed to the rock, that is there's always a ripple sitting right behind that rock, but the actual water molecules are moving right through that ripple."

Although it's tricky to get a sense of it in Cassini's latest picture, the wavy ripples that Daphnis creates are in fact three-dimensional features. "Daphnis actually has an orbit that's slightly inclined so it kind of slowly moves up and down relative to the rings," explains Cuzzi. "As it does this these perturbations that it causes on the edges are actually flipped up vertically." Indeed previous long-range images of Daphnis taken by Cassini — when the ring system was lit nearly side-on by the Sun — have shown the waves throwing shadows across the icy material below.

Tiny Moon, Huge Influence

What's abundantly clear from Cassini's new image is that even a diminutive moon like Daphnis can have a dramatic effect on the rings. Yet there are even smaller inhabitants of the rings that Cassini's recent orbits have been revealing in exceptional detail. And though these objects may be tiny, and their interactions with the ring system less obvious, they still could have an important story to tell us.

As Cassini was making another one of its ring-grazing orbits on 18 December last year, it turned its wide-angle camera towards a section of the A ring. The image it captured revealed a blizzard of artefacts from radiation and cosmic rays striking the camera's sensor. But it was the subtle features that the picture also revealed embedded within the immense, striated, swathe of icy material that were of interest to Cassini's scientists. Across much of the frame were numerous small, bright streaks within the rings — features known as 'propellers'. Cassini has been scrutinising propeller features in the rings ever since it first spotted them during the early phases of its time at Saturn, says Tiscareno. They come in two types, essentially large ones and small ones. "These are the smaller ones," he says. "We call this part of the ring the 'propeller belts'. They're just swarming here."

The bright streak of the propeller itself is caused by the gravity of a tiny, icy, moonlet disturbing the material around it. "You should probably think of the moonlet as a snowball about the size of a football pitch [roughly 100m]," says Tiscareno. There's even something of a connection between the propellers and their fellow ring-inhabitant Daphnis. "The propellers here and the gap that Daphnis is orbiting in are fundamentally the same thing," explains Tiscareno. "The only thing is that with these propellers [the moonlet] tries to start excavating a gap in the ring, but the ring is so massive that it fills the gap back in before it is able to extend all the way around."

Tell-tale Blades

The December 18th image represents Cassini's finest view yet of the smaller propellers. But Tiscareno and his colleagues have also been using the close ring-grazing orbits to capture spectacular pictures of some of the larger propellers — those that are thought to be created by slightly more substantial icy moonlets. On February 21st the spacecraft imaged one such example informally dubbed 'Santos-Dumont' by the mission team. The image is shown above; although it does not reveal the moonlet itself, it shows fine detail in the 'blades' of the propeller structure that the moonlet has made within the rings.

"This propeller is one of about a half-dozen whose orbits we know well enough that we had the ability to target them with flyby imaging, and it is one that turned out to be passing relatively close by during this particular flyby of the Cassini spacecraft," says Tiscareno. "The central moonlet is the size of a city block [around 500-1,000m], and the disturbance it creates in the rings can stretch for a few thousand kilometers, though it's only a few kilometers wide."

What is it, then, that studying the detailed nature of these features can tell researchers? Why might the Cassini team be using this time in the mission's final months to capture images like those of Santos-Dumont and the propeller belts? Part of the answer is that the propellers could illuminate our understanding of an enigmatic process that we have much to learn about. "It opens a window onto how planetary systems form because, when you have a baby planet forming itself out of the disc around [a] nascent star, it's a very similar situation to this moonlet that's embedded in the disc of Saturn's rings," explains Tiscareno.

It's not just with the propellers that Cassini's ring-grazing orbits are offering broader insights either. One recent high-resolution image reveals what Cassini scientists call 'straw' — conglomerations of icy material that have gathered to form huge clumpy structures within the rings. Examining this 'straw' in detail could shed light on how icy rubble 'sticks' together, which in turn could tell us something about planet formation says Cuzzi. "There are lots of things, big-picture problems, that we are understanding better by looking at the rings." he adds.

Edging towards the end

On April 22nd, once Cassini has completed its ring-grazing orbits, it will switch to a final set of trajectories that the mission team have dubbed the 'Grand Finale' orbits. These will take the spacecraft between the inner edge of the ring system and Saturn itself, with the last orbit hurtling the spacecraft into the planet's atmosphere. As the probe loops around the planet, Cassini will still be gathering data of immense interest to researchers back on Earth. "We're going to be directly measuring the mass of the rings," says Tiscareno. "That will help us distinguish between different models that we have for the origin and operation of the rings and might give us more clarity on how old the whole ring system is."

Cassini will also acquire unprecedented radar observations of the ring material. And its dust instrument will analyse the particles' chemical composition says Cuzzi. "So, finally, we'll be able to answer the big question that we've always had: why are the rings red," he says. "They're actually not white, like pure ice should be, they're actually a little red and we really don't know why that is."

Cassini's grand finale promises to be a period of intense excitement tinged with inevitable sadness then. But perhaps it's Cuzzi who best sums up the spirit for the weeks and months ahead: "We're definitely not done yet," he says.

Cassini's Orbital Timeline

October 1997 — Cassini launches from Cape Canaveral in Florida, US.

July 2004 — The spacecraft enters into orbit around Saturn.

June 2008 — The probe finishes its primary mission. It moves into a new set of orbits for Saturn's equinox in summer 2009.

September 2010 — The Equinox Mission complete, Cassini starts its Solstice Mission orbits, many of which take it far from Saturn.

November 2016 — Cassini starts its series of close 'ring-grazing' orbits. 22 April 2017 - The 'Grand Finale' trajectories will begin; Cassini will dive between the inner edge of the rings and Saturn itself.

15 September 2017 — The mission will come to an end as Cassini enters Saturn's atmosphere.

ABOUT THE WRITER
Will Gater is an astronomy journalist and presenter. Follow him on Twitter at @willgater.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Our Sun is an oddball: most stars don't exist alone. But sociability has consequences, writes Mark A. Garlick.

By ESO/L. Calçada (http://www.eso.org/public/images/eso1540a/) [CC BY 4.0], via Wikimedia Commons

Like living organisms, stars are a social bunch. Of the 20 star systems closest to the Sun, only 12 are solitary. Stellar multiplicity is very common, and our seemingly lonesome Sun drew a short straw.

If the Sun were reduced to the size of a pea, the closest stars would still be hundreds of kilometres away. So when we consider the truly enormous scale of our Galaxy, it is obvious that stellar multiplicity cannot be the result of neighbours just passing by and becoming entangled by gravity. Though this does happen, it's phenomenally rare. The inescapable conclusion is that most stars have companions because that is how they are formed.

Stars in binaries are commonly quite far apart from each other. They might be separated by less than an astronomical unit (approximately 150 billion km, the Earth-Sun distance) or they could be hundreds of times further apart, taking centuries to complete their orbits around each other. We call this latter group detached binaries. This is where both stars occupy their own Roche lobes — the region where matter is gravitationally bound to the particular star — without spilling over and influencing its companion.

Yet often the situation is very different. If two stars are sufficiently close together when one evolves into a red giant, the atmosphere of this evolving star can stretch beyond its Roche lobe and actually reach the companion. This creates drag, which brings the stars spiralling together and makes for a much more dynamic system — what is called an interacting or semi-detached binary — with two or more stars engaged in a frenetic gravitational tug-of-war. This situation can lead to some extreme behavior.

A distorted demon

Algol (Beta Persei) is the first example of an entire class of semi-detached star systems, hence collectively known as Algol binaries. The two stars are huddled close together, with a separation comparable to their radii and orbital periods ranging from hours to (more typically) days. This proximity means that one of the stars, usually one that has entered the late stages of its life causing it to greatly expand, is distorted by the gravity of its companion, which is usually more massive, hotter, brighter and still in the prime of life. The larger star is so expanded it is said to fill its Roche lobe. Gas from the secondary component flows towards the primary and strikes its surface on the equator. The impacting gas is then flung off, somewhat like water bouncing off a spinning ball, and spreads out around the primary to form a tenuous, messy outflow around it.

Algol binaries are variable stars, and we know of thousands of them. The variation comes from the fact they are eclipsing binaries as seen from Earth: when the secondary star passes in front of its smaller but brighter companion, the brightness dips significantly making the star flicker.

However, in cataclysmic variables we find a much more extreme semi-detached binary. Cataclysmic variables are a very broad class that includes novae and dwarf novae. The two components are almost always the same: a red dwarf and a white dwarf. These two stars are so compact that typically the entire system would fit within the bounds of our Sun. They swing around each other in a matter of hours. As in Algol binaries, one of the stars, the red dwarf, fills its Roche lobe. Gas from this star flows towards the voracious white dwarf — 10 billion tonnes of it every second — forming what is called an 'accretion disc' around it.

It is the accretion disc that gives these systems their dynamic properties and puts the cataclysm into their name. As material in the disc spirals towards the white dwarf, friction heats it to extreme temperatures, making these systems very bright in the ultraviolet and sometimes X-ray regions of the electromagnetic spectrum. Sometimes the accretion disc become unstable, suddenly dumping more gas than usual onto the white dwarf. Alternatively, there might be a momentary, rapid increase in the amount of gas being fed into the disc from the secondary. Both situations can cause a huge influx of extra material accreted by the white dwarf, which then flares up to produce a dwarf nova outburst. The amount of time between such events can vary from days to years. In even more extreme cases, the gas accumulated by the white dwarf becomes so hot and dense that the outer layers undergo thermonuclear burning, as in the centre of a star. This is a classical nova. The event is sudden and explosive, and typically destroys the accretion disc but neither star. In time, the disc will grow again and the 'cataclysm' will repeat.

Not all cataclysmic variables have accretion discs, however. Sometimes the white dwarf is highly magnetic — around 10,000 times more so than a typical bar magnet. This is strong enough to disrupt the formation of the accretion disc, resulting in a ring instead. These systems are known as 'intermediate polars'. In 'polars', where the white dwarf's magnetic field is stronger still, even a ring cannot form. In this instance, gas escaping from the secondary latches onto the white dwarf's magnetic field lines and flows towards it in great auroral arcs.

From powerful to phenomenal

X-ray binaries are more powerful still. As the name suggests, these systems are bright X-ray sources. It's a slight misnomer in that cataclysmic variables are also often X-ray powerhouses, but X-ray binaries tend to be much more luminous at these wavelengths, for reasons that will become clear.

In appearance cataclysmic variables and X-ray binaries are quite similar: a large star sometimes filling its Roche lobe, losing gas to a compact companion, often &mdsah; but not always — through a disc. The distinction is that in X-ray binaries the compact primary is a neutron star or a black hole, rather than the white dwarf found in cataclysmic variables. This extra degree of compactness is what gives them their awesome power.

In cataclysmic variables, the gas in the accretion disc reaches very high temperatures as it spirals around in the disc towards the white dwarf. But neutron stars are hundreds of times smaller than white dwarfs, and black holes are tinier still. This means that the gas orbiting in X-ray binaries travels a lot closer in towards the compact star, picks up much more speed and so more kinetic energy, and experiences much greater frictional heating. The energy released when this gas accretes onto the neutron star or black hole is phenomenal. Some X-ray binaries emit as many X-rays as thousands of Sun-like stars combined.

X-ray binaries exist in two flavours. If the secondary star is lightweight, such as a red dwarf, astronomers call the system a low-mass X-ray binary. But in some cases the mass-donating star is a massive giant, in which case they are called high-mass X-ray binaries; black hole system Cygnus X-1 is an example. The class as a whole resembles cataclysmic variables in that one of the stars fills its Roche lobe. But what happens when both stars fill their respective lobes?

The two members touch at the inner Lagrangian point, causing the system to resemble a gargantuan dumbbell. Because each star is in contact with the other, astronomers refer to these as contact binaries. A famous example is W Ursae Majoris. Binary systems such as this one exchange atmospheric gases and share a sheath of gas, or envelope, and eventually they settle into a configuration where each star has the same temperature. Usually the stars are yellow to orange in color (spectral types F to K) with orbital periods ranging from five to 20 hours. Often one or both of the stars are highly magnetic, and large star spots may be present as a result. These systems are true cannibals. In time, the larger star will completely consume the envelope of its smaller, luckless cohort, laying bare its core. Eventually even this is swallowed in a final merger, until only a single star exists where previously there were two.

Roche Lobes

The delicate balance of gravity is key to understanding binary stars

The Roche lobe is the teardrop-shaped region around a star in a binary system, within which gas is gravitationally bound to the star. But at the point between the two stars where the lobes meet — the inner Lagrangian point (L1) — gravity and centrifugal forces cancel out and the gas feels no net force. That is unless one of the stars has expanded to the point that it fills its Roche lobe. This happens in cataclysmic variable and many X-ray binaries. In these cases, the atmosphere of the lobe-filling star is pushed beyond the L1 point and flows towards and around the other star. As the escaping gas stream encircles the star it eventually loops around and collides with itself. This causes it to lose energy, spread out and form an accretion disc around the companion star.

Accretion Discs

Many powerful phenomena come not from stars, but from the dusty discs around them

There are many kinds of astronomical objects that grow or evolve by gravitationally attracting and harvesting nearby material, a process termed 'accretion'. The accretion disc is simply what we call the gathered material. It is the machine that surrounds an object and allows it to grow larger and more massive. For example, stars are born at the centre of protoplanetary discs, illustrated above. As dust and gas orbit in the disc, it loses momentum and spirals into the central regions, where it accumulates.

In binary stars, accretion discs are created when a secondary star fills its Roche lobe and spills material into the lobe surrounding an adjacent primary star. The gas leaves the inner Lagrangian point and runs in a narrow stream towards and around the primary star, creating a ring-like flow. Friction in this ring causes the gas to heat up, converting potential energy into kinetic energy. The gas also loses angular momentum, so it drops down to lower orbits and spreads slowly inwards, forming a fully fledged disc. The inner regions of an accretion disc around a stellar mass black hole can have temperatures measuring millions of Kelvin — hot enough that they emit most of their energy as X-rays. Astronomers find these emissions useful because they can detect the disc easily and thus infer the presence of a black hole, even if the latter emits no radiation. Supermassive black holes also exhibit accretion discs, although they are orders of magnitude larger and cooler.

ABOUT THE WRITER

Mark A Garlick is a writer and illustrator and animator specializing in astronomy. His latest book is Cosmic Menagerie: A Visual Journey Through the Universe.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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Top Tips For Stargazing

Follow this practical advice and enjoy a good first night under the stars.

Image released under Creative Commons CC0 public domain, courtesy of Pixabay.com.

1. The eyes have it

Forget the myth that to be a 'proper' astronomer you need to have a telescope — this is complete rubbish! There are myriad things you can see with the naked eye alone — from the constellations to meteor showers, the band of the Milky Way and even the occasional galaxy. If you want to take things further, consider investing in a pair of binoculars before a telescope — you'll be able to see more of the night sky without dealing with the practicalities of setting up.

2. Keep out the cold

We know it's not rocket science (if you'll excuse the pun), but astronomy involves a lot of time outdoors being still, so it's important to stay warm. Several layers of thin clothing are recommended, as are waterproof shoes, a hat and gloves. If you have pages to turn or equipment (especially touchscreens) to operate, fingerless gloves are ideal.

3. Give your neck a rest

If you stand still staring up at the sky you'll soon find that you get neck ache. So avoid the pain entirely by finding something that you can lie back on. A reclining garden chair or an old-fashioned deck chair are ideal, but your spine will thank you even if all you have on hand is a camping groundsheet, a yoga mat or a waterproof picnic blanket to spread over the grass.

4. Accustom your eyes

If you go outside from a brightly lit room you'll probably only see a handful of stars so it's vital to wait and let your eyes adjust to the darkness — ideally for 30 minutes — and you'll notice an incredible difference. Doing so should allow you to see much fainter stars.

5. Use a star chart

These are a great way to learn your way around the night sky. Astronomy magazines publish star charts every month or you can buy a book. You can begin by identifying patterns of bright stars. From there you can gradually learn your way around the constellations, and before too long they'll become familiar and you'll be able to navigate your way around the night sky without reference to a book or chart.

6. Bring a red flashlight and a compass

A red-light flashlight is a must when you've given your eyes time to adjust to the dark but still want to see your star charts. This is because dark-adapted eyes are much less sensitive to red light than they are to white. You can buy a red-light night vision flashlight, or make one by taking a regular flashlight and sticking a piece of red acetate over the front. A compass will help you find north, which is essential not only when using star charts but also in setting up your telescope mount.

7. Stay away from streetlights

If you can, head out to the countryside to take advantage of properly dark skies. But if you are observing in an urban area, shield yourself from any artificial light sources, as they will prevent your eyes from acclimatizing to the dark.

8. Slow and steady

No one has ever looked at the night sky and instantly understood how to find their way around; there really is a lot to see up there! Not even the legendary Sir Patrick Moore was immune to this — he honed his knowledge by memorizing one new constellation each night.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Shooting Stars

Spotting a meteor streaking across the sky is a truly captivating sight to behold.

By C m handler (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

You may know of meteors as 'shooting stars', but the truth is there is nothing stellar about them. The dramatic, bright trails that streak across the sky come from a much more harmless source — a dust particle the size of a grain of sand colliding with Earth's atmosphere, making it glow.

You will see several random, or 'sporadic', meteors an hour on any clear night, but a better way to catch them is during one of the annual meteor showers. These occur when Earth passes through the debris trail of a long-gone comet — a path of dust waiting to burn up in our planet's atmosphere.

Meteor showers are named after the constellation they appear to come from — and, sometimes, the closest star. Most major showers will be active over a period of at least a few days — and some for a few weeks. But they have what's known as a 'peak' — the night when you can expect to see the greatest number of meteors. The rates can vary quite a lot, but prominent displays, such as the Perseids, can produce an average of one meteor a minute under clear, moonless skies at their peak. There is also the chance a particularly dense patch of dust could lie along the path of debris, creating a surge in meteor numbers.

How to view

The best time to observe is shortly after midnight on the date when peak activity is predicted, when the sky is darkest and Earth's rotation faces the direction of the planet's motion in space, so the oncoming meteors seem to travel even faster.

As with any other form of observing, the best place to view is away from light pollution, so find as remote a location as possible and give your eyes at least 20 minutes to get really used to the darkness.

Don't look directly at the constellation that the meteor tracks appear to come from, concentrate your gaze high in the direction of the darkest portion of the sky that's free from obscuring trees and buildings. If the Moon is in the sky, try to make sure it's not in your field of vision or reflecting off walls or windows, as this will seriously degrade your night vision.

If you need to look at star charts or books to find your bearings, use a dim red light rather than a white one so that you don't lose your night vision. If you use a smartphone app, place a red cellophane filter over the screen.

Making meteors

By the time a comet approaches Earth, the Sun's heat has evaporated ice in its nucleus. This releases dust that follows the comet and, over time, can be spread out along all of the comet's orbit. When Earth intercepts this dusty path, lots of particles collide with the atmosphere and we see a meteor shower.

Meteor diary

Quadrantids

Peak: Around 3 January

Max possible activity: 120 meteors per hour

Activity window: Early January

Eta Aquariids

Peak: Around 6 May

Max possible activity: 60 meteors per hour

Activity window: Early May

Perseids

Peak: Around 12 August

Max possible activity: 80 meteors per hour

Activity window: Mid July to mid August

Orionids

Peak: Around 21 October

Max possible activity: 26 meteors per hour

Activity window: Mid to late October

Leonids

Peak: Around 18 November

Max possible activity: Usually 15 meteors per hour but can be higher

Activity window: Mid to late November

Geminids

Peak: Around 13 December

Max possible activity: 110 meteors per hour

Activity window: Mid to late December

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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Amanda Doyle looks at the evidence for life amid Europa's apparent plumes and examines the missions that could deliver proof

Europa by NASA's Planetary Photojournal

Europa is the smallest of Jupiter's Galilean moons, its strange icy surface riddled with fractures. But it is what lies beneath the surface that is of most interest to scientists: in September 2016, Hubble captured images of finger-like projections coming from Europa's limb.

One possible explanation for these findings is plumes of water vapour bursting out from Europa, a theory that is supported by earlier Hubble observations in 2012, when its spectroscope identified water vapour in the moon's south polar region. Both observations are strong evidence that Europa boasts a subsurface liquid ocean, making the moon one of the best places in the Solar System to search for alien life.

The first evidence for Europa's subsurface ocean came from the Galileo spacecraft. Jupiter's immense gravity causes a tidal bulge to be raised on Europa, and this tidal heating is sufficient to cause some of the ice to melt below the surface. Magnetometer readings from Galileo showed that Europa has an induced magnetic field, which can only occur if there is a medium in which a current can travel, such as salty water.

Water in the aurora

In 2013, a team led by Lorenz Roth from the Southwest Research Institute in Texas announced the detection of what appeared to be a plume rising into space in data. They used the spectrograph on Hubble to determine that an ultraviolet auroral glow from Europa's south pole — observed in 2012 — was possibly caused by water molecules being broken apart by Jupiter's powerful magnetic field.

Artist's Concept of Europa Water Vapor Plume
by NASA/ESA/K. Retherford/SWRI

The latest observation was announced in September 2016, when further evidence for these plumes was revealed. Initially searching for a tenuous atmosphere surrounding Europa by viewing the moon transiting in front of Jupiter, William Sparks from the Space Telescope Science Institute was surprised to find traces of a water plume.

"By an interesting coincidence, Roth and the team announced their discovery of evidence for plumes using [Hubble] STIS spectroscopy within a couple of weeks of our transit program beginning," said Sparks. "Our approach is independent, but that changed the landscape and people started looking right away for plumes."

Sparks' latest observation of the plumes adds weight to evidence for an active water cycle on Europa, but is this an environment that could support life? There are three key ingredients for life as we know it, and water is only one of them. The correct 'biogenic elements' need to be present in order to provide the building blocks for life and an energy source is also considered essential.

If life on Europa were to avail itself of photosynthesis as an energy source, it would have to be situated near the surface, where ice is potentially thin enough for sunlight to filter through. However, living near the surface has its pitfalls, as radiation from Jupiter would likely exterminate anything unprotected by thick ice.

As on Earth, so on Europa?

In the pitch-black depths of Earth's oceans, hydrothermal vents spew out enough hot material for ecosystems to thrive despite never seeing sunlight. If similar vents were to exist on Europa they could provide a safe haven for life. It is unknown how the tidal heating occurs on the icy moon but if the heating were to penetrate to the core, then the flow of heat up from the ocean floor could create vents. However, if the heating is restricted to the upper layers of ice, then venting would not occur.

It may seem far-fetched that life could exist in freezing conditions on Europa, but we know that there is microbial life on Earth that is extremely resilient to such hostile environments. Microorganisms are known to survive in Antarctic ice by producing their own antifreeze, and lakes situated far below the ice also have microbial life.

If some form of life exists on Europa, then could it be detected? "If the biomass in the plumes were high enough, it may be possible to find biosignatures," Sparks explains. "A more likely approach — and plumes are very relevant — is that presumably most of the plume material gets deposited back on to the surface. Along with all the other places on Europa where material appears to have seeped out onto the surface, that would certainly be a place you'd want to look."

The best way to explore Europa and the tantalising possibility of life would be to send a lander with a powerful drill, which would ultimately drop a probe into the ocean below. Such an ambitious project is still many decades away, but there are missions planned which will take the first steps in revealing the moon's secrets.

ESA's Jupiter Icy Moons Explorer (JUICE) is not a life-finding mission, but it does have the ability to finally confirm the existence of the subsurface ocean on Europa, as well as measure the thickness of the ice shell. JUICE will also explore the chemistry of the moon to ascertain if it has the right chemical soup needed for life. Meanwhile, NASA is planning the Europa Multiple-Flyby Mission, also known as the Europa Clipper. While the goals of this mission and JUICE are similar, the NASA mission will spend more time focused on Europa. There is also the possibility that this mission will include a small lander.

Both missions will further our knowledge of the surface of Europa and what lies beneath, thus paving the way for a mission dedicated to finding life.

Drilling Deep

The technology for drilling through Europa's thick ice crust has been tested

Drilling through the Antarctic ice to the lakes below is an excellent testbed for studying the type of life that might exist beneath Europa's surface, as such organisms are cut off from the atmosphere and from sunlight. These Antarctic lakes are kept in liquid form due to the immense pressure from the ice above.

There have been numerous drilling expeditions to such subglacial lakes, and the first successful breach of the overlying ice occurred in February 2012 when a Russian team reached the waters of Lake Vostok, some 4km below the ice. DNA analysis of the surrounding ice has shown that microbial life likely exists in the lake, although this has yet to be confirmed from the lake water itself.

Not all expeditions are so lucky. On Christmas Day in 2012, a UK-led project to explore Lake Ellsworth failed when they were unable to drill through the 3km of ice above the lake.

In 2013, an American team had more success when they broke through 800m of ice to reach Lake Whillans. There is also an extensive network of streams, and the entire area covers around 60 square kilometres. Analysis of the lake water revealed nearly 4,000 species of microbes.

Examining Europa

Several planned missions will further our knowledge of whether the icy Jovian moon's environment is right for life

James Webb Space Telescope
The James Webb Space Telescope (JWST), due to launch in 2018, will have the capability of confirming the existence of plumes of water emanating from Europa. It will also be able to observe Europa in regions of infrared light that are invisible to Hubble. If water plumes do indeed exist, JWST will detect the water signatures in the infrared. These observations are impossible from Earth, as the water vapour in the atmosphere blocks the view. However, as the plumes appear to be intermittent, it may be difficult to time JWST observations just right in order to detect the plumes.

Europa Multiple-Flyby Mission
NASA's mission to Europa was approved in 2015 and a suite of nine scientific instruments has been announced for the orbiter. These include high-resolution cameras, spectrometers, an ice-penetrating radar and a magnetometer. The latter will be used to determine the depth and salinity of the ocean by measuring the direction and strength of Europa's magnetic field. Thermal mapping of the surface will also reveal any recent eruptions of warmer water from below the ice. The mission is due to launch in the 2020s, and will perform 45 flybys of Europa over three years, with the orbits varying from a height of 25km to 2,700km.

Jupiter Icy Moons Explorer
ESA's Jupiter Icy Moons Explorer (JUICE) is due to launch in 2022 and reach the Jovian system in 2030, spending three and a half years studying the moons of Jupiter. It will perform two flybys of Europa before moving on to Callisto and then eventually settling into an orbit around Ganymede, the main focus of the mission. JUICE will study surface features on Europa to ascertain how they formed. By thoroughly analysing the Jovian system — including Jupiter itself — JUICE will shed light on planet formation and the conditions needed for life to emerge on icy moons.

About the Writer
Amanda Doyle is a postdoctoral researcher at the University of Warwick and editor of the SPA's quarterly magazine.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

For hundreds of years, astronomers have pondered whether there is any truth to testimonies of a glow illuminating the dark side of Venus. Paul Abel explores this centuries-old astronomical anomaly

Cloud structure in the Venusian atmosphere in 1979, revealed by observations in the ultraviolet band by Pioneer Venus Orbiter - NASA Photo Gallery Venus

Over the past decade, our space missions have revealed some spectacular things about the worlds in our Solar System. We've seen water fountains on Enceladus, methane lakes on Titan and vast icy mountain ranges on Pluto. We know more about the other worlds that orbit our Sun than at any other point in human history.

Yet in spite of that, one of our nearest neighbours continues to tease us with a 400-year-old mystery. The ashen light of Venus is rather like an astronomical ghost story: it would be easy to dismiss the phenomenon as a romantic relic of a bygone era were it not for a small number of consistent observations made by seasoned planetary astronomers well into the 21st century. As we see Venus return to our evening skies, it brings this ancient puzzle, and now is a good time to ask: will we ever solve the riddle of the ashen light?

The story starts in the 17th century. On the evening of January 9, 1643, Italian astronomer Giovanni Riccioli turned his telescope towards Venus. On that date Venus would have appeared as a crescent, with a phase of about 29 per cent. As Riccioli looked, he noticed that the dark side of the planet — which is normally invisible — appeared to be glowing with a faint greyish light that he called 'The ashen light of Venus'.

The next reported sighting came in 1714 when William Derham, who was a Canon of Windsor, observed it with his telescope and described the ashen light as a 'dull rusty colour'. Sir William Herschel also observed the phenomenon on a number of occasions. The British astronomer Thomas William Webb caught sight of the light on January 31, 1878 with his 9.4-inch reflector. Using magnifications of 90x and 212x, he noticed that the light had a slight brown-ish cast. Webb may well have been the first person to recommend using an eyepiece with an occulting bar — a device that hides the brilliant crescent to reduce glare.

Many sightings, little proof

There were many sightings of the ashen light in the 20th century: in 1940, 1953, 1956 and 1957 a number of observers reported sightings on consecutive nights to the British Astronomical Association. Dale Cruikshank, a planetary scientist at the NASA Ames Research Center together with William K. Hartmann, also a planetary scientist, made an interesting observation of Venus in 1962. On November 12, 1962 at 7pm, when Venus was at inferior conjunction, both Cruikshank and Hartmann observed the night side of the planet enclosed within a thin ring of light (this would have been the extended cusps of Venus). The night side seemed to be glowing with a brownish colour, quite different from the surrounding blue sky. The effect was not uniform and appeared to be strongest closest to the thin crescent.

Sir Patrick Moore was another veteran planetary observer who recorded the ashen light. Although he sighted it numerous times during his long observing career, the event that convinced him of the reality of the light occurred on May 27th, 1980. Using his 15-inch reflector at 300x magnification, Patrick described the effect as 'striking', with the ashen light strongly resembling the effect of earthshine on the Moon.

One of the great problems with the ashen light is that it has never been photographed or imaged; all observations are visual and so there is no tangible proof that the phenomenon is real. Yet not all visual observers have been able to view it. Edward Emerson Barnard, for example, never managed to see it. I have been observing Venus regularly for over 18 years and I have never managed to see the ashen light.

A number of amateur astronomers now believe that it is merely an illusion. It is reasonable to suppose that under certain conditions the brilliant crescent of Venus combined with poor seeing tricks the human eye into thinking it can see the night side of Venus, when in reality it is not visible.

Those who believe in the reality of the ashen light have suggested a number of ideas as to its cause. We can probably dismiss the suggestion of 18th-century German astronomer Franz von Paula Gruithuisen, however. He believed the light to be caused by fireworks of the Venusians celebrating the ascension of a new emperor.

More theories, more problems

A more reasonable idea has been advanced that the thick atmosphere occasionally thins in places, allowing the hot surface to be seen. The problem is that this would only be visible in the infrared part of the spectrum, well beyond the threshold of the human eye. The idea that the ashen light is the result of multiple rapid lightning strikes in the upper atmosphere of Venus can likewise be dismissed, since the flashes would be too faint to be seen from Earth.

The only viable idea left is the oxygen emission theory. This suggests that when oxygen atoms combine in the planet's upper atmosphere on the night side of Venus, they emit light. This has been observed by two Soviet spacecraft, Venera 9 and 10. Moreover, the variability of oxygen emission might explain why the ashen light is not always observed.

It seems likely that the enduring mystery of the ashen light will not be settled until the phenomenon is imaged. Only then will we be able to say with any real confidence whether it is really a product of Venusian metrology or an artefact of the human visual system. As Venus becomes well placed in the evening skies at the start of 2017, now might be your chance to catch a glimpse of it — and decide.

Seeing is Believing

How to maximize your chances of catching the elusive ashen light

No one can say when or if the ashen light will next appear, but looking at the observational records a number of interesting things stand out. First, it seems that the light is more frequently observed when Venus is an evening planet (eastern elongations), but even then it is not sighted during every elongation and there can be many years between reports.

The phase of Venus has to be below 30 per cent, so mid February onwards would be the time to start looking. The ashen light can only be viewed in a dark sky, which means the seeing conditions are likely to be less than ideal. Don't use a really high magnification unless the seeing conditions allow for it. Personally I find about 150x quite suitable. It might be worth trying some filters, too. Observers who have seen the light report that orange and green filters may enhance the effect if it is present. It is important to realize that the brilliant crescent will give rise to all manner of spurious optical effects. Some observers get round this by using an eyepiece that contains an occulting bar. Hiding the crescent behind the bar can reduce the glow, but even then you need to be cautious.

Most reports indicate that the ashen light takes the form of a coppery brown glow on the night side of Venus. The glow may cover all of the night side, or just a part of it. If you suspect the light is present, try taking an image of it and of course, alert other astronomers so that other independent images can be taken. If you have more than one telescope, try imaging it with one and observing it with another, and make a drawing so you can compare what you have seen with what you have imaged. Finally, send your observations to the Mercury and Venus section at the British Astronomical Association (https://britastro.org/sections) so that they can be studied and analyzed by professional astronomers.

Imaging the Crescent Venus

Pete Lawrence reveals how capture the planet's crescent on camera

Imaging Venus against a dark sky through a telescope produces tricky imaging conditions, with multiple reflections and unwanted aberrations. Catching it with the Sun up, or immediately after sunset is a good way to tame the planet's brightness, the lighter sky reducing contrast.

A monochrome high frame rate camera with a red or infrared-pass filter is a good choice for this photo, as it makes the blue sky appear dark. These longer wavelengths also less affected by poor atmospheric seeing. Detail in the planet's clouds is tricky to record, normally achieved using either an ultraviolet-pass filter (around 350nm) or an infrared-pass filter (1,000nm plus). Be aware that some telescope coatings are quite effective at blocking ultraviolet light, and so produce a blank disc.

The basic imaging procedure is to centre the planet, focus accurately and capture a high frame rate recording. As Venus is bright, keep the frame rate high and the gain low, recording several thousand frames. Process the capture with a registration-stacking program such as AutoStakkert!.

The bright crescent can be captured using a DSLR camera attached to a telescope or by using the afocal technique of pointing a camera down the telescope's eyepiece.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Astronomer Will Gater delves into the incredible astrophysics behind some of the season's most famous luminaries

Betelgeuse by Reid H.

Betelgeuse

Of all the stars in the winter sky, Betelgeuse (Alpha Orionis) is arguably the one that prompts the most excitement and intrigue. To the eye it looks like a sparkling, orange-hued point of light, but decades of scientific study — some conducted using the most powerful astronomical facilities in existence today — have shown that a thrilling story is unfolding far away.

"Betelgeuse is a red supergiant with a radius in optical light of about 4.5 astronomical units — in other words, almost the size of the orbit of Jupiter," says Dr Anita Richards, who has studied the star as part of her research at the University of Manchester's Jodrell Bank Centre for Astrophysics.

Betelgeuse hasn't always been this bloated, ruddy leviathan however. It was once a hot O-type star, like Mintaka in Orion's Belt is. It would have had a blueish-white color and would have also been more massive than it is now — perhaps around 20 times the mass of the Sun.

"Such massive stars have much hotter cores than the Sun with faster nuclear fusion, using up most of their hydrogen [in] a few million years," explains Richards. "Fusion [of] heavier elements such as helium and carbon takes over, but the outer layers cool and expand; the increase in size means that the luminosity grows as the star becomes redder."

It's this process that has created the Betelgeuse we know today, but it's what will happen at the end of its life that excites many astronomers. "It will probably take at least a hundred thousand years for Betelgeuse to exhaust [its] fuel for nuclear fusion," says Richards. "Finally when it runs out, its inner layers are no longer supported by radiation pressure and collapse, releasing roughly as much energy in an instant as the Sun radiates in 8,000 million years — a supernova."

This violent detonation will be a truly breathtaking sight in our skies. "It will be brighter, as seen from Earth, than any other supernova in recorded history so far," says Richards, "as brilliant as the full Moon and visible in daylight."

Where to find it
Betelgeuse is easily visible on the left shoulder of Orion as you look at it with the naked eye. Key to finding it is identifying Orion itself, which is probably best achieved by locating the unmistakable trio of stars known as Orion's Belt. Betelgeuse is just under 10° to the north-northeast of any of them.

Rigel

Like its bright companion Betelgeuse, the brilliant star Rigel (Beta Orionis) is a supergiant, nearly 80 times the size of our Sun. But even to the naked eye there's one striking difference between these two stellar behemoths: their colors. Betelgeuse is orange-white while Rigel sparkles with a blue tint. Why the difference? It all comes down to their temperatures. The hotter a star is the bluer it tends to shine, while cooler stars glow more red. And indeed Betelgeuse's surface temperature is about 3,300°C while Rigel's is roughly 11,800°C.

Where to find it
Rigel is one of the few stars in the winter sky that is so bright that it can be seen easily from heavily light-polluted city centres and suburban areas. From a dark-sky site it is a blazing point of light at the right foot of Orion.

W Orionis

Less famous than either Betelgeuse or Rigel, the scientific story behind the star known as W Orionis is no less intriguing. It has an atmosphere that swirls with large amounts of carbon.

"For a star to become carbon rich, something called the dredge-up needs to happen several times so that carbon from the inner parts of the star gets to the surface and [is] released to its atmosphere," explains Dr Lizette Guzman Ramirez, an ESO Fellow based at the Leiden Observatory in the Netherlands.

This churning has occurred within W Orionis as it has aged. The carbon can absorb blue wavelengths of light from the star; this, combined with its relatively cool temperature, means it has an exquisite red hue — something that's obvious through a telescope.

Where to find it
Although it's on the cusp of naked-eye visibility, it's easier to hunt down mag. +6.1 W Orionis with binoculars. One way of finding it is to imagine a rough equilateral triangle tilted on its side, the base of which is marked by Mintaka and Bellatrix (Delta and Gamma Orionis). W Orionis is at the apex.

Practical project
The deep red of W Orionis is a wonderful sight to see, but it's even clearer in photos. In this project we'll use a simple astrophotography technique to bring out the star's striking color and all you need is a DSLR, a lens with a focal length of 50mm or similar and a static photo tripod. First mount your camera on the tripod, check W Orionis is in the view and then focus the image. Then take four or five 30-second exposures and stack them together in software such as Startrails to create an image that shows the star field 'trailing' as the Earth rotates. By using a 50mm lens you should be able to capture some of Orion's other bright stars in the field of view and so when you compare their trails to that of W Orionis the remarkable ruddy hue of the latter should be very obvious.

The Trapezium Cluster

Cast your eyes towards the stars of Orion on a crisp winter's night and you may — if you're far enough away from the ravages of light pollution — be able to glimpse a fuzzy star at the heart of the Hunter's sword. What you are seeing is in fact not a star but the magnificent Orion Nebula, M42. This enormous, sprawling, mass of dust and gas clouds some 1,350 lightyears from us shines in our night skies due to a cluster of hot, young stars embedded within it, known as the Trapezium Cluster.

These infant stars are thought to have emerged from the nebula roughly one million years ago. Their story began as material in the nebula coalesced together to form dense clumps within the then cold, dark clouds. These clumps grew and grew until nuclear fusion reactions fired up in their cores and the stars within the cluster were 'born'.

As the stars started to shine they began to emit huge amounts of powerful radiation, which streamed out into the gas and dust around them. Slowly a vast cavern — whose sweeping walls glowed brightly due to this onslaught of intense ultraviolet radiation — was sculpted into their maternal nebula too. And that's what we see when we look at the Trapezium Cluster and the beautiful Orion Nebula around it today: an extraordinary tableau of star formation sketched in ethereal celestial light across the winter sky.

Where to find it
The Trapezium Cluster sits within the bright central part of the Orion Nebula, which is itself located within a pattern of stars often referred to as Orion's Sword. The easiest way to find M42 is to scan your telescope south from the central star in Orion's Belt, called Alnilam (Epsilon Orionis), by a little over 4° until you come across the nebula and the embedded cluster.

Practical project
Few celestial objects are as captivating as the Orion Nebula seen from a dark-sky site, but for keen stargazers just starting out in astronomy spying the four most prominent stars of the Trapezium Cluster, within M42, is a rite of passage; so in this project we're going to cover a few additional tips for tracking them down. Assuming you've managed to locate the Orion Nebula in your telescope using our tips above, the first thing to note is that the Trapezium itself is much smaller in angular diameter than you might think — you'll need to use a magnification of at least 75-100x to get a pleasing view of it. As we've already mentioned, the cluster resides in the brightest part of the nebula, but if you need another signpost to it, look for the nearby 'dark' region of nebulosity that 'points' the way to it.

Aldebaran

Compare Aldebaran (Alpha Tauri) to Betelgeuse and you'd be forgiven for thinking that the two are very similar stars — they're alike in color and not very different in brightness. Both are swollen, ageing stars in fact, but Betelgeuse is much more massive. "Aldebaran is only about 1.3 times the mass of the Sun," says Dr Anita Richards. This means that Aldebaran's eventual demise will be very different from Betelgeuse's. Instead of creating a supernova it will slowly shed its outer layers to form a beautiful glowing planetary nebula with a white dwarf at its centre.

Where to find it
At the start of January Aldebaran is high in the south at around 21:45 UT. The V of the Hyades star cluster is a helpful signpost to the star, but if you have trouble finding that use an imaginary line extending northwest from Orion's Belt to point you in the direction of the stars of Taurus, and thus the Hyades.

Sirius

No discussion of the science of the winter stars would be complete without mentioning dazzling Sirius, the alpha star of Canis Major. There's no other star that rivals it in the heavens at this time of year, and it's the brightest star in Earth's night sky full stop. So why does Sirius appear so impressive in our skies? Well, it's a relatively bright star in itself but it's also very close to us too at a distance of 8.6 lightyears. To put that in perspective, brilliant Rigel in nearby Orion is over 100 times farther away!

Where to find it
Though Sirius may be bright, if you're new to astronomy finding which one of the dazzling stars in the winter sky it actually is can still be a challenge. Thankfully there's a little trick you can use. If you can find the much more recognisable Orion's Belt, it actually 'points' in the direction of Sirius, if you follow the line of the belt down from right to left.

The Pleiades

If the Trapezium Cluster in the Orion Nebula is a vision of the birth of stars, then the magnificent Pleiades, or M45, in the constellation of Taurus shows what happens as these glittering collections of stars age and evolve. After open star clusters emerge from their maternal nebulae they drive away the gas and dust around them before slowly scattering into the surrounding Galaxy.

That's precisely what we're seeing when we look at the many members of the Pleiades, which are thought to be 125 million years old — we're looking at a grouping of young stars that are no longer swathed in the dense, often glowing, nebulosity associated with their formation. Over time the stars within the Pleiades will likely disperse further.

In fact it's thought that our very own star, the Sun, may have once belonged to a star cluster like M45. Astronomers believe they've even been able to track down one of the Sun's siblings, a star within the constellation of Hercules known as HD 162826. Its composition and orbital history within the Milky Way matches the Sun's, yet it is now 110 lightyears from us.

Where to find them
The Pleiades sit about 14° to the northwest of the bright star Aldebaran. At the end of January you'll find the cluster high in the southwest sky around 21:15 UT. If you can't spot it with the naked eye try scanning along a line roughly northwest from the Hyades star cluster with a good pair of binoculars.

About The Writer
Will Gater is an astronomy writer and journalist. Visit his website willgater.com and follow him on Twitter at @willgater.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

How a Frenchman's 18th-century list of objects to avoid became the definitive catalog for amateur astronomers

Messier 13 by Laurie A.

For budding and seasoned stargazers in the northern hemisphere, the Messier Catalog is the most famous observing list of astronomical deep-sky objects. Within the 110-strong catalog are examples of every known deep-sky object — a good assortment of galaxies, open and globular star clusters, nebulae and one supernova remnant: the famous Crab Nebula in Taurus, which is also the first object in the catalog. It bears the designation Messier 1, commonly written as M1.

Messier's catalog has become so ingrained into astronomical lore that objects are commonly described by their Messier number. So 'M42' is often used in place of, or in addition to, the name of the object, in this case the Orion Nebula.

The irony of this useful catalog is that it was never intended to be a list of objects for observers to hunt down with their telescopes: rather, it was a list of objects to avoid. This is because Charles Messier, the French astronomer who created the catalog, was a comet hunter, and many comets appear as faint, fuzzy blobs in the sky — just as deep-sky objects do. So he assembled these deep-sky objects into a list of 'red herrings', in order to make sure they could be discounted during his cometary searches. He conducted these in his observatory, a wood and glass structure atop a tower in the medieval Hôtel de Cluny in Paris.

Growing Number
The Messier Catalog first arrived on the scene in 1771 as a list of 45 objects. Ten years later it had been expanded to 103, with some of the later observations being undertaken by Messier's assistant Pierre Méchain. The catalog stayed at this size for over 100 years. There were some interesting developments in the 20th century, as astronomers and historians made seven additions to the list. These were not just arbitrary objects, but ones that Messier and Méchain made observing notes about shortly after the final version of the catalog was published. It was only in 1967 when M110, a faint dwarf elliptical galaxy in the constellation of Andromeda, made its way into the catalog as the final officially recognised object.

There are several reasons why Charles Messier's 'list of objects to avoid when looking for comets' has become so readily accepted as targets to seek out with a telescope. One is that it isn't too long: 110 objects makes it a nice, manageable number. So manageable, in fact, that some amateurs like to undertake Messier marathons, where they endeavour to observe all 110 objects in one night.

Another reason is that Messier used a variety of different sized scopes in his comet searches, including a 3.5-inch refractor. The objects in his catalog don't need massively powerful instruments to be seen: they're within reach of small amateur telescopes.

Finally, it's a reasonably comprehensive list, encompassing almost all of the wondrous sights that novice stargazers would wish to see, many of them bright objects.

Of course, the Messier Catalog is not the only list — there are more than 110 objects out in space after all. The New General Catalog (NGC), for example, lists nearly 8,000 objects, followed by an extension known as the Index Catalog (IC) that adds more than 5,000 on top. You'll also find that many objects appear in multiple catalogs: M42, the Orion Nebula, is also designated as NGC 1976. However, the NGC and IC lists are little more than databases of deep-sky objects. They have less appeal for amateur astronomers because many of their entries are too faint to see without a professional telescope.

There is, however, one other list that's worth a mention: Patrick Moore's own compilation, the Caldwell Catalog. This is, in effect, an extension to the Messier Catalog. It includes many more bright, deep-sky objects that are perfect for you to train your telescope on from your back garden.

Top Naked-Eye Messier Objects

M42
RA 05h 35m 17s dec. -05° 23' 28"
The Orion Nebula is a vast cloud of dust and gas — what's known as an emission nebula, and is a star-forming region. It's easy to spot with just your eyes as a misty patch below the three belt stars in the constellation of Orion.

M45
RA 03h 45m 48s dec. +24° 22' 00"
The Pleiades, also known as the Seven Sisters, is an open star cluster in the constellation of Taurus. Depending on your eyesight and how dark the sky is at your location, you'll be able to see between six and 12 stars.

M13
RA 16h 41m 42s dec. +36° 28' 00"
The hundreds of thousands of stars that make up the Great Globular Cluster in Hercules are just visible to the eye from dark locations. It's one-third of the way south of a line between the stars Eta and Zeta Herculis.

M31
RA 00h 42m 42s dec. +41° 16' 00"
The Andromeda Galaxy is without doubt the most distant object visible to the naked eye, being about 2.8 million lightyears away. Find it in the constellation of Andromeda as a faint smudge in very dark, Moonless skies.

Top Small-Scope Messier Objects

M81
RA 09h 55m 33s dec. +69° 03' 55"
Looking at Bode's Galaxy in the constellation of Ursa Major with a 3- to 4-inch scope, you'll see it as the brighter of two fuzzy patches close to each other in the night sky. The second patch is another galaxy, the fainter M82.

M51
RA 13h 30m 00s dec. +47° 16' 00"
The Whirlpool Galaxy in the constellation of Canes Venatici is a face-on spiral galaxy. Small scopes reveal the basic shape and the smaller companion with which it is interacting. Larger instruments reveal more structure.

M3
RA 13h 42m 12s dec. +28° 23' 00"
This globular cluster, also in Canes Venatici, is an easy target for a small telescope - though it can be tricky to locate. It's one of the largest and brightest globulars in the sky; a small scope will reveal great detail and a compact core.

M57
RA 18h 53m 35sdec. +33° 01' 45"
The Ring Nebula in the constellation of Lyra is a shapely planetary nebula, and one of the easiest of its kind to observe. With a 3- to 4-inch scope it's easily seen as a misty but quite defined oval patch.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

The Moon isn't the only object orbiting the Earth you can take a look at

International Space Station by Jimmy E.

There are two types of satellite visible in the night sky — natural ones like our Moon and artificial ones that we have placed up in orbit. Of all the artificial ones, the International Space Station, or ISS, is probably the best known. Easy to predict, its constant, often bright passage across the heavens is a sight that instills wonder.

Humankind's orbital outpost typically appears as a dot, which gets brighter as it passes across the sky before fading again. Sometimes the ISS appears bright and then fades abruptly from view. The fading occurs when the ISS's trajectory takes it into Earth's shadow, and as most sightings tend to be in the early evening the disappearance occurs when the ISS has reached the eastern half of the sky. If you're an early riser, Earth's shadow will be to the west. This causes the ISS to instantly 'switch on' as it passes out of the shadow back into full sunlight.

Solar power
It's the interaction of sunlight with the surface of a satellite that makes things interesting. Spacecraft that have large reflective areas can flare in brightness, sometimes quite significantly. The best flares are caused by a group of satellites known as the Iridium constellation: 'constellation' being the collective noun for a group of satellites. When you see one of these spacecraft brighten rapidly, this is what's known as an Iridium flare.

The science behind the flare is unremarkable in that each satellite in the constellation has three large flat, reflective antennas. When the Sun's light happens to hit an antenna at the right angle, it will appear bright when seen from a fairly localised region on Earth's surface. What is remarkable, however, is the fact that there are ways to predict, with down-to-the-second accuracy, when a flare can be seen from your location. And we're not talking faint, indistinct flaring here: some Iridium flares can increase the apparent brightness of the satellite's dot from that of a dim star to something brighter than Venus.

The brightest flares tend to be around mag. -8.0, brilliant enough to easily illuminate any thin clouds that may get in the way. In theory, such a bright pass could even cast shadows — not that anyone ever looks behind them when a flare occurs! Not all Iridium flares will reach this brightness, of course; the flare may not be optimal and you may be located away from the position on Earth where the brightness of the flare peaks.

Other satellites can also show flare activity and it soon becomes obvious, especially to meteor imagers, that flaring spacecraft occur all the time. A flaring satellite that reaches peak brightness and is then rudely truncated by the camera shutter closing will look very similar to what you'd expect to see from a bright meteor trail.

It's possible to tell the difference by looking carefully at the brightest end of the trail. If the trail looks perfectly smooth and is cut off squarely at the brightest end, then it's either a rare meteor trail interrupted in its prime or — much more likely — a flaring satellite trail that wasn't allowed to complete its display before the camera shutter closed. Iridium flares also tend to record as white trails, while meteor trails often exhibit a pink start changing to green — an effect caused by the excitation of atoms in our atmosphere.

There are over 1,000 operational satellites orbiting Earth and an estimated 21,000 objects larger than 10cm. If you widen the net and include objects down to 1cm in size, the count moves beyond half a million. In fact, on any clear, moonless night, it would be unusual not to see an artificial satellite passing through the constellations, appearing as a moving dot among the stars.

Predicting a pass
There are many different ways to predict satellite passes — some more reliable than others.

Heavens Above
One of the most popular and respected methods is to use the website Heavens Above (www.heavens-above.com). You can create a free account that logs your location and generates visibility predictions for many different satellites. Sky charts accompany visible passes, and clicking on the date of the pass will typically bring up an all-sky chart showing the passage of the satellite among the stars. So long as you have a basic knowledge of the constellations then the track, adjusted for your location, should be pretty easy to identify. As an added bonus, if you don't know the stars that well, then this is a good way to have some fun while learning the night sky.

Other Prediction Sites and Apps
For the slightly more technically minded, there are many excellent programs available to download such as WXTrack (www.satsignal.eu/software/wxtrack.htm), which is able to predict the passage of many satellites directly from a Windows PC. Apps for other operating systems, including smartphones are also available; many are listed in a 'satellite tracking software index' at celestrak.com/software/satellite/sat-trak.asp. Some of these programs are commercial, requiring you to purchase a licence to use them, but there are plenty of freeware options available too.

Ensuring Accuracy
One problem with computer predictions is reliability. This could be down to problems with the program itself, or that you haven't set your location, date or time properly. And if satellite data isn't updated regularly, this too may affect accuracy. If doubts start to creep in, compare the predictions for an easy to identify satellite, such as the ISS, with Heavens Above. If they don't match, update the software's satellite data, and your time and location details, before trying another program.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

The two huge gas giants are home to a staggering number of natural satellites

Jupiter's Moon callisto Cast Shadow Onto Jupiter's Cloud Top by Kim Mitchell

Jupiter is grandiose in all respects. Not only is it the largest of the planets — it would take 1,321 Earths to fill the volume of Jupiter — it's also more than likely that it keeps the largest entourage of moons. There are 67 that we know of, and though many of these are fairly small and can't be observed from Earth, the biggest four are easy to spot with just a small pair of binoculars.

These are Io, Europa, Ganymede and Callisto: the Galilean moons, so named because they were spotted by Galileo in the early 17th century.

A minimum size pair for spotting these four moons would be 7x50s, which magnify what your eyes see seven times and have front lenses that are 50mm in diameter. Your view will be much improved by resting the binoculars on a wall or fence, or even attaching them to a tripod with an inexpensive bracket. Through a 3- to 6-inch telescope the moons will appear brighter and fill more of the field of view. Don't worry if you don't see all four: as the moons travel around the planet they may be behind or in front of Jupiter when you're looking.

It's by using a larger scope with a front lens over 6 inches that you start to see detail on the planet itself, and this includes the occasional shadow cast by the Galilean moons.

Moon with a View

Fellow gas giant Saturn has 62 known moons, but only seven are visible. Due to its sheer size, the easiest of Saturn's satellites to see is Titan. This moon has a diameter of 5,150km, which makes it bigger than the planet Mercury. In the moon rankings, it's the second largest in the Solar System, only beaten by Jupiter's Ganymede. It's also the only moon with a substantial atmosphere. When you're gazing at it through your scope, you're not actually looking at Titan's surface but at its nitrogen-rich cloud tops. In terms of brightness, Titan can reach mag. +8.4, putting it well within the reach of binoculars, while with a small telescope you'll have no trouble seeing it.

The remaining six moons are all within the grasp of a 6-inch scope. In order of brightness, after Titan comes Rhea, which shines at mag. +9.7, Tethys at mag. +10.3, Dione at mag. +10.4, Enceladus at mag. +11.8 and then quirky Iapetus.

The unusual nature of this last moon quickly became apparent to its discoverer in 1671, the Italian astronomer Giovanni Cassini. He first saw the moon on the western side of Saturn but found it missing on a later search, when it should have been on the eastern side.

It wasn't until 34 years later, when telescopes had improved, that Cassini finally saw Iapetus to the east, because when it's here it's almost two magnitudes fainter. This is why it had been impossible to see it before. Cassini deduced, correctly, that this was because the moon has one very bright hemisphere and one very dark one, and is also tidally locked to Saturn.

This means, like our Moon, it always shows the same face to its planet. It follows that we see a different part of Iapetus from our Earthly viewpoint when it is to the east or west of Saturn. As a result, Iapetus varies between mag. +10.1 and mag. +11.9. However, the faintness trophy goes to Mimas, which at mag. +12.9, needs perfect viewing conditions without any light pollution to see comfortably.

Jupiter's famous Galilean moons

IO

Diameter: 3,640 km

The tremendous gravitational pull of Jupiter on this innermost of the four Galilean moons, together with its closeness to the planet, means Io whizzes round Jupiter in just 1.75 Earth days. This fast orbital speed is easily seen in a small telescope: it visibly shifts position in just a few hours.

Europa

Diameter: 3,140km

The second Galilean moon out from Jupiter, Europa should theoretically be visible with the naked eye as it shines at mag. +5.3. But Jupiter's overwhelming brightness means it's difficult to separate moon from planet. Europa's brightness is due to its smooth, icy surface, with perhaps an ocean underneath.

Ganymede

Diameter: 5,260 km

The third major moon out from the planet is not only Jupiter's biggest, it's also the largest moon in the entire Solar System — but only by a whisker. This is a world with a cold ice surface, a large warm ice (possibly water) mantle, a rocky interior and a liquid iron core.

Callisto

Diameter: 4,820 km

The last of the four giant Galilean satellites is Callisto. It is the third largest moon in the Solar System, after Titan, the biggest of Saturn's moons. Callisto's entire icy, ancient surface is covered with impact craters that date right back to the time of the early Solar System.

Saturn's best moons to observe

Titan

Diameter: 5,152 km

The largest of Saturn's moons has a 16-day orbit. At its farthest, you'll find it about five of Saturn's ring diameters from the planet, mag. +8.4 at its brightest, which makes it visible in good binoculars. Titan makes up over 96 per cent of the mass of everything orbiting the planet.

Rhea

Diameter: 1,528 km

The second largest moon of Saturn, ninth largest in the Solar System, and currently the 20th catalogued in distance out from the planet. It makes an orbit in 4.5 days, reaching just under two ring diameters from Saturn. It is mag. +9.7, making Rhea an easy target for a 3-inch refractor telescope.

Iapetus

Diameter: 1,469 km

This is the third largest and most distant of the main moons of Saturn. Its 79-day orbit, which is the most inclined of the inner satellites, takes it out to 12 ring diameters from the planet. The visual magnitude ranges from +10.1 to +11.9, so Iapetus needs about a 6-inch scope to see it at its darkest.

Dione

Diameter: 1,123 km

This moon orbits up to 1.5 ring diameters from Saturn over 2.7 days. Its visual magnitude of +10.4 makes it visible on dark nights with a 3-inch refractor. This is the densest of the moons, meaning it may have a large rocky core. Helene and Polydeuces, two smaller moons, share its orbit.

Tethys

Diameter: 1,060 km

This moon orbits about one ring diameter away from the planet and takes 1.9 days to do so. It has a magnitude of +10.3 and so can be seen in a 3-inch refractor. Tethys has a great canyon that stretches three-quarters of the way round the moon, and two co-orbital moons, Telesto and Calypso.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

The movement of the atmosphere can affect your ability to observe stars and planets to a surprising extent

The weather is generally considered to be the biggest hindrance to astronomy. What's the betting that the night you decide to head out for the night that spell of fine weather changes for the worse? So you'd have thought that when the skies finally clear, your problems would be over. Surprisingly, though, even a clear night may not be the best time to go out and observe.

The issue is the 'seeing'. In astronomy, this doesn't mean how you look at something. It's a term that describes how much the view you see through your telescope is disturbed by what's going on in the atmosphere above you.

At times of good seeing, you'll get sharp, steady views through your telescope. But bad seeing produces turbulent, unstable telescope views of the Moon and shuddering, shaky images of stars. On the other hand, deep-sky objects like galaxies and nebulae aren't as badly affected by bad seeing.

This is thanks to the layers of moving air between you and the object you're looking at, the effects of which are magnified by your telescope. In the atmosphere, air at different temperatures is always moving around and mixing together. Light travels through hot and cold air at different speeds, so it is continually bent this way and that before it finally arrives at your telescope all shaken and stirred.

Sometimes there are very few moments of clarity. One of the best ways to see this distortion is to watch the Sun setting on a clear horizon. It will have a jagged appearance, thanks to the sunlight moving through layers of turbulent air.

The other factor that affects observing conditions is the transparency of the night — just how clear the sky is. After it's been raining, the sky is transparent because the rain clears away particles of dust and smog from the air. However, when it's been raining it also tends to be windy, which means that the seeing is bad. You'll notice that the stars are twinkling because of this. Transparent conditions are, however, good for large, faint objects like nebulae and galaxies, which really benefit from the better contrast. Poor transparency generally means the air is steady with good seeing, but dust and particles are sitting in the still atmosphere. These conditions are good for looking at the Moon and stars.

A good way to think of seeing and transparency is to imagine a swimming pool with a coin resting on the bottom. The water represents our atmosphere and the coin the starry object you're looking at. Through completely still water with no currents, the coin looks still, crisp and clear. In this case the seeing is perfect and so is the transparency. If the water is made to move — causing ripples — the coin's image will shake around; the transparency is still good but the seeing is bad. And if some milk is spilt in the pool so you can't see the coin very clearly, the transparency will be reduced.

It goes to show that you're at the mercy of the atmosphere ... and that moments of clarity are a wonderful thing.

Clear and present

You can't do anything about 'high-level seeing' — the air currents far above you — but you can influence the 'low-level seeing' to create steadier air conditions immediately around you and your scope. Here's how:

1. Leave your scope outside to cool to the ambient temperature, eliminating any air currents in the tube.

2. Observe on grass rather than concrete. Concrete absorbs more heat from the Sun and radiates it out to the air above it for longer.

3. Air currents tend to stay low to the ground, so it can be a good idea to raise up your scope on a platform.

4. If you build an observatory, make it using thin materials such as wood that can cool quickly.

5. The geography of your observing site affects how air behaves. Being near the sea gives you calmer air than if you're near a range of hills, where air is forced upwards, causing turbulence.

Using the Antoniadi Scale

It's very useful to note down what the seeing is when you're observing. Many astronomers use the Antoniadi scale as a measure of what the atmosphere is up to. It's a five-point scale using Roman numerals. I indicates the best conditions, while V describes the worst.

I. Perfect seeing, without any quiver of turbulence whatsoever.

II. Slight shimmers; moments of stillness last several seconds.

III. Average seeing; larger air tremors blur the view.

IV. Poor views, with constant troublesome undulations of the image.

V. Bad views with severe undulations; so unstable that even quick sketches are out of the question.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Eight of the biggest astronomical myths, collected and comprehensively busted to help you become an expert in no time at all

Meteor (Perseid's) and M45 (Pleides) by Mark Bell

The Moon can't be seen in the daytime
There's a common conception that just as the Sun can only be seen in daylight hours, the Moon only comes out at night. But Earth's rotation means that the Moon must be above the horizon for 12 hours out of every 24, regardless of the length of the night. As such, the Moon is often somewhere in the daylit sky. Whether we see it is down to two things — its altitude in the sky and its phase.

Polaris is the brightest star in the sky
Polaris is certainly among the most famous, being the star closest to the north celestial pole, but this usefulness does not make it the brightest in the sky. Spend an evening outside and it will become obvious that this honor falls to Sirius, in the constellation of Canis Major.

Stars twinkle
'Twinkle, twinkle, little star' has a lot to answer for. Stars often appear to flicker in the night sky, but this has nothing to do with the star and everything to do with our turbulent atmosphere. Once it reaches Earth, starlight is reflected, bent and contorted by this turbulence, until it reaches your eye. Viewed from space, stars would not twinkle at all.

Earth's distance from the sun causes the seasons
Not so — Earth is actually closest to the Sun during the northern hemisphere's winter. The real reason is due to Earth's 23.5-degree axial tilt, which means each hemisphere gets varying durations of sunlight over the year.

Polaris has always been the pole star
Polaris' position next to the north celestial pole is a temporary one, a result of Earth wobbling on its axis as it spins. The change is about 1 degree every 72 years, with a full cycle taking around 26,000 years. In 3,000 BC the pole star was Thuban in Draco, but in 2,000 years time it will be Errai in Cepheus.

Shooting stars are really stars
If you have ever wished upon a star, you may be shocked to learn it wasn't a star at all. What you saw was the bright flare of a piece of debris, likely to be no bigger than a grain of sand, burning up in our atmosphere. They are properly known as meteors. If a fragment makes it to Earth's surface, it is called a meteorite.

The point of a telescope is to magnify celestial objects
While telescopes can make the denizens of the night sky appear bigger, this isn't their primary purpose. Their main function is to gather light, using a lens or mirror depending on the design, so that we can see objects too dim to view with the naked eye.

The Moon has a dark side
The phrase 'dark side of the Moon' is often and erroneously used to refer to the Moon's far side, which means something subtly different. The far side is the hemisphere of the Moon permanently turned away from Earth, but calling it the dark side implies it never sees any sunlight — which is not the case. The lunar far side goes through the same cycle of phases as we see on the near side from Earth, with the only period it can technically be called the dark side being the time of full Moon.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Is your son or daughter the next Patrick Moore? We look at ways you can encourage the astronomers of the future!

Winners of the 2015 SCAS Striking Sparks program pose with their Orion XT6 Classic Dobsonian telescope awards alongside proud sponsors, teachers and parents.

Ever since I can remember I have loved astronomy. As a boy of seven I used to gaze out of the window at the stars, curious about their names and the patterns that make the constellations. I learned much by myself, but it wasn't until I started at secondary school that, through some friends, I was introduced to our local astronomical society.

If, as a child, you had particularly encouraging parents who already knew something about the subject or were curious enough to learn with you, you were off to a good start. Joining an astronomical society is the perfect next step in the stargazing journey. These clubs offer friendship and experience — not to mention access to telescopes — and could even provide the spark that leads to a career in astronomy.

Summer Stargazing

Many societies take a break in August, but that's not because there's no astronomy to be done. In fact, for kids especially, this time of year has quite a number of benefits for stargazing. Though it doesn't get dark until fairly late there's no school to worry about, so a couple of late bedtimes on clear, starry nights hopefully won't be too much of a problem. Plus, the nights are usually considerably warmer at this time of year, so even though you still have to wrap up, you don't need to suffer the coldness associated with winter stargazing.

You don't need a telescope either: many fine deep-sky objects, such as globular cluster M13 in Hercules or the Coathanger asterism in Vulpecula, can be seen with a good pair of binoculars.

On that note, though, one thing that has massively improved since my early stargazing days is technology. One great tool is the video telescope eyepiece. This is linked to a screen to give live feeds of what the telescope is seeing &mash; particularly handy if you're out stargazing with several children and would rather not have them come to the eyepiece single file.

If you're thinking of running a star party for your kids, make sure you have a back-up plan in case the weather takes a turn for the worse. A space quiz with some chocolate prizes goes down a storm!

Wow-Factor Sights

The Milky Way

Equipment: Naked eye.

Where it is: Visible from summer through Christmas, running across the sky from the south to southwestern horizon.

What you'll see: A misty meandering river of light — it's made up of the combined light from millions of stars. For the best views, head out to a countryside location.

Fun fact for kids: This is just the visible section of our Galaxy, which contains between 200 and 400 billion stars in total.

The Pleiades

Equipment: Naked eye or binoculars.

Where it is: In the constellation of Taurus, the Bull.

What you'll see: This open cluster is known as the Seven Sisters, which is roughly the number of stars you can see with the naked eye. It's also a lovely sight in binoculars, which will reveal several dozen more stars.

Fun fact for kids: This family of several hundred stars sits about 400 lightyears from Earth.

The Moon

Equipment: Binoculars or telescope.

Where it is: Varies, but close to the ecliptic.

What you'll see: Head outside when the Moon is in a crescent or gibbous phase to see craters, mountains, valleys, escarpments, rilles and more. Steer clear of the time around full Moon - there are too few shadows to reveal the incredible surface detail on our satellite.

Fun fact for kids: The surface of the Moon covers roughly the same area as Africa.

Great Events for Kids

Be Galileo (or Einstein, or whoever!)
Instead of just having a general talk on, say, Galileo, why not ask around the club for someone with thespian tendencies? They could dress up and play the famous Italian astronomer, describing his own inventions and discoveries. It's a simple way to liven up the subject for young minds and you could have a lot of fun, too.

Treasure hunts
One meeting could be created as a themed 'mission', with stations around the society's hut or field containing challenges that need to be solved to complete the mission. By doing so, the younger members of the club would get to understand some aspect of astronomy. Each station could hold riddles, puzzles or simple questions.

Space writing, poetry or drawing competition
You don't need to narrow this one down, just allow minds to run wild! The competition could be inspired by a talk, such as the 'Be Galileo' event. You could also open it up to local schools, in which case the local newspaper might be interested. Put up a small telescope as a prize and the publicity could bring in some new faces to your club.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

The Moon was made way back when a large chunk of cheddar the size of Mars hit Earth. True? No! Hold on to your Double Gloucester as this myth, and others, are about to be disproved!

Sea of Serenity by Craig Heaton

To state a fact: the Moon is always around somewhere in the sky at some time or other. It sounds obvious, but this concept is wrapped up in urban myth and provoked a great discussion among planetarium presenters recently. The myth in question has two parts, both of which are entirely wrong: firstly, the Moon comes out at night; and secondly, it's invisible during the day. No names will be mentioned here to protect the guilty, but I was told by a science teacher just the other day (which makes the following even worse to absorb), that the myth is taught in a particular primary school because the pupils would be uncomfortable with the truth. I'd suggest that maybe the wrong teacher is in charge of science.

Myth-Busting

Understanding the Moon's orbit around Earth and the corresponding way it is lit by the Sun, which leads to its phases, is not easy. However, with a bit of patience it is possible to appreciate why the Moon can be visible during the day and does not only 'come out' when it's dark at night.

The question really should be: why don't we notice the Moon during the day? The simple answer is that the sky is brighter during the day than at night, so the Moon is not as prominent. There are lots of other reasons why, such as the fact that evenings are the part of the day when we generally have more time to gaze at the sky, whereas we're all busy rushing around during the day.

So, yesterday, after one such busy day at work I took the time as night approached to do some stargazing and watched the full Moon rise over the trees in the field in front of our house. To the naked eye, this is when the Moon is most magnificent: a low, golden-tinged globe slowly being carried into the sky by the rotating Earth. It's when the Moon is low that it's possible to notice this movement the most and, if you have time, it's worth noting where it is an hour later — you may be surprised how far it has moved.

A couple of other things that are deserving of special attention are the Moon's color and its movement across the sky as it orbits Earth.

The Moon moves at a blistering Mach 3, which is three times the speed of sound at sea level. The stronger goldish-to-reddish color of the rising Moon, as opposed to the grey-white view when it's higher, is explained by the fact that when it's low to the horizon, light from the Moon gets filtered through Earth's atmosphere. All the particles that make this up scatter the blue light, which leaves mostly red light to reach us when we're watching the spectacle on the ground.

A Moving Moon

As for the Moon's own travels, try and find a star very close to its left side. An hour later the Moon will have passed over the star, which should now be sitting to the Moon's right. The Moon may not completely cover the star, sometimes the star will just graze its top or bottom. You'll have more success seeing this if the Moon is not full, as its light washes out most nearby stars.

The passing of the Moon in front of the star or planet, blocking it, is known as an occultation and these are listed in the handbook of the British Astronomical Association. If you've never seen a star being blinked out by the Moon, then you have an assignment — go out and see one! Even better is a planet: Venus or Saturn are my favorites. Saturn is especially good: with a scope you can watch as the rings are slowly covered by the Moon, dipping in and out of the lunar valleys before finally disappearing.

Earthshine

The Sun is the main object that lights the Moon, but Earth also has an effect. Our planet is over 3.5 times the diameter of the Moon, so we reflect more light onto its surface than the Moon gives us when it is full. This is called earthshine and it can be seen as a faint glow on the unlit part of the Moon when it is a thin crescent (before and after a new Moon).

Phases of the Moon

The word Moon is responsible for our word 'month': one mooneth (or thereabouts) was the measurement of the time it took for the Moon to complete one orbit of the Earth in relation to the Sun. Although it's given in schools as 28 days, the Moon's changing appearance (it's cycle of phases) takes just over 29.5 days. This is known as the Synodic Month. It represents the period from one full Moon to the next (or any other identical phase, for example half Moon to half Moon).

The Sun is always shining on one half of the Moon — how much of the lighted side we see depends on where the Moon is in orbit around Earth. The new Moon happens when the Moon sits between us and the Sun, and so the far side is lit (this is also the only time a solar eclipse can occur).

As the Moon moves around Earth and each day passes, we see more and more of its lighted side, a waxing (growing) evening crescent first, then half Moon, waxing gibbous and finally full Moon. At this point, the Moon sits on completely the opposite side of the sky to the Sun. Now everything reverses and the waning (shrinking) phases go through gibbous, half and waning morning crescent, finally back to new.

Observing the Moon

The Moon: it's big, round and bright. Anyone can discover its finer details, whether it's with the naked eye or binoculars.

Some astronomers seem to get a complex about the Moon. It's not that they're affected by it in werewolfish ways, but rather they develop a loathing for our large, rocky satellite. Why? Well, these usually friendly astronomers come to see it as a natural light polluter, washing away all the faint, small and fuzzy galaxies and nebulae they like to view. To them, the Moon is more of a nuisance than an object that's worthy of observing.

This is a real shame as the Moon has so much to offer. There's simply no truth in the assertion that when 'you've seen it once, you've seen it all' — with binoculars and small telescopes the appearance of the Moon can change dramatically from one hour to the next. Another reason it's so good is that it's easy to find. There's no star-hopping or fiddling with finderscopes, as the Moon quite plainly hangs about just waiting for you to look at it.

Magnify the view

The Moon is a stunning object to look at, but there are times when binoculars or a telescope are the only things that'll do it justice: for example, the first few days after new Moon through to just before full Moon. During this period, when the Moon is waxing, we see a sunlit, happy side and a contrasting unlit, spooky side.

The views of the bright side give us the names of the phases: crescent, half, gibbous and full. After full Moon the phases reverse as it starts waning; these are equally worth a look. However, the post-full phases are generally seen very late in the night, when most people prefer to sleep.

The zone between the light and dark sections of the Moon is known as the 'terminator', and this is the place to concentrate on for the most stunning lunar views. It's along the waxing Moon's terminator that, if you were standing on the lunar surface, the Sun would be rising. The low light hits its mountains, craters, valleys, crinkly ridges, rilles, escarpments and all manner of other volcanic and impact features, casting dramatic shadows across the stark landscape. The view is further enhanced by largely flat, dark areas of solidified lava known as the lunar seas, over which shadows can stretch for tens of kilometres. All of this gradually changes as the Moon spins on its axis, but even at this slow rate you will be able to see hour-by-hour movement.

That the Moon spins on its axis may seem strange, as we know the same side always faces Earth. We are actually able to see 59 per cent of its surface as the Moon 'wobbles' up and down and from left to right, an effect known as libration.

We only see the one face because a long time ago the molten material inside the Moon caused it to become tidally locked to Earth. This 'synchronous rotation' means that the Moon spins once on its axis in exactly the same time it takes to orbit Earth. You can get an idea of how this works if you imagine yourself observing from the Sun. Over the course of a month you would see the Moon spin once.

Of course, leaving Earth takes a bit of mastering, but once you can imagine it, understanding the Universe becomes a breeze.

Latin Lingo

When you look at a map of the Moon, you'll notice that its physical features all have Latin names because they were named a long time ago when Latin was more widely used. Here's what those names mean in modern English.

Lunar Atlases

There are many atlases and wall charts vying to help you find the various craters, mountains and features of the Moon. They have their strengths and weaknesses, and you'll find some easier to use than others.

Watch out for any that flip the Moon so that south becomes north, or make any other change to orientation. These are fine for seasoned astronomers who use a specific telescope setup to observe the Moon, but for those of us who switch between correcting lenses, terrestrial telescopes, binoculars and the like, go for a plain and simple map with north at the top. It's also an advantage to have one with high-quality pictures.

Wall charts are also good for getting a general idea of where things are on the Moon. However, they're less use at the eyepiece unless they're safely wrapped up in a dew-proof coating, so it's worth getting a laminated version.

Experiencing Eclipses

Why do eclipses occur so infrequently? It all has to do with the Moon's tilted orbit.

Over the course of a year the Sun moves across the sky on a path known as the ecliptic. It rises in the east and sets in the west, in essence appearing like it travels around Earth.

If the Moon orbited Earth in this same plane, then each month we would get an eclipse of the Sun (when the Moon passes between the Sun and Earth) and an eclipse of the Moon (when the Earth is between the Sun and the Moon). We don't, however, as the Moon's orbit is tilted at an average of 5° from the ecliptic.

Most months this means that from our point of view on Earth, the Moon moves above or below the Sun at new Moon, and above or below Earth's shadow at full Moon. We only get an eclipse when the Moon's orbit intersects the ecliptic and all three bodies are in the correct alignment.

Due to a fantastic coincidence, the Sun is 400 times bigger than the Moon, but around 400 times further away. This means that they appear to be the same size. The Moon just covers the Sun during a total solar eclipse, allowing us to witness its ghostly outer atmosphere, known as the corona.

Top Ten Moon Sights

Our celestial neighbour has enough to keep astronomers busy for a lifetime, but here are 10 highlights for telescopes and binoculars.

Crater Grimaldi
Size: 173km across
Type: Basin
Appearance: Visible even to the naked eye, this dark basin reveals fantastic detail through binoculars and telescopes, such as eroded walls, ridges and low hills.

Rimae Sirsalis
Size: 425km long
Type: Rille system
Appearance: This series of fault lines is visible even in a small telescope, which will reveal Sirsalis's main crack running straight for over 300km through a cratered environment.

Crater Copernicus
Size: 94km across
Type: Impact crater
Appearance: One of the Moon's recognizable features and the result of quite a recent impact, a scope reveals terraced crater walls and central peaks rising from the floor below.

Vallis Alpes
Size: 155km long
Type: Valley and rille
Appearance: A clean gouge through a mountainous region, the 18km-wide fault line can be easily visible in small scope and binoculars as a dark stripe in a lighter landscape.

Crater Plato
Size: 109km across
Type: Lava-filled impact crater
Appearance: In binoculars and small telescopes the beauty of this crater is its jagged rim with 2km high mountains compared to its smooth lava-filled floor.

Montes Alpes
Size: 3.4km maximum height
Type: Mountain range
Appearance: Through binoculars you will just be able to make out this rangle of peaks; with a telescope they start to reveal really good detail, especially if the terminator is close by.

Montes Teneriffe
Size: 2.5km maximum height
Type: Mountain range
Appearance: When caught in the right angle of sunlight this 110km-long mountain range reveals good detail among its peaks using a small scope and around 150x magnification.

Mons Piton
Size: 2.2km in height
Type: Mountain
Appearance: Lying on its own in the flat region of the Mare Imbrium, use a small telescope when the Sun's illumination is low to reveal the shadow cast by this lone peak.

Rupes Recta
Size: 110km long
Type: Rille
Appearance: This popular target for binoculars and small telescopes is another fault line where the lunar surface suddenly drops by 300m. It's best seen when close to the terminator.

Vallis Rheita
Size: 450km long
Type: Valley
Appearance: A long, wide valley that many think is the result of a sustained meteor bombardment. A small telescope will show the crater Rheita next door has a central peak.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Groups of stars against the blackness of space, clusters make great observational targets for the amateur astronomer

M3 Globular Cluster by Doug Hubbell

When you gaze up at the night sky, it looks like a lot of stars are on their own. But a solitary-looking star may be a member of a vast group that's travelling through space as a unit. If we wind the clock back millions of years, we may find these stars forming in the same vast cloud of dust and gas.

Known as open clusters, these families of anywhere from a few dozen to a few thousand stars are created in the dusty spiral arms of our Galaxy. They travel together through space, but gentle tidal forces eventually cause the stars to move apart until they begin to merge into the general starry background.

There are many fine examples of newer and older clusters out there, perfect for looking at with binoculars. As a rule of thumb, you can pretty much assume that the younger the open cluster, the more compact it appears, since the stars haven't had much time to drift apart.

There is another variety of star cluster out there: the globular cluster. These are much bigger than the open sort, consisting of hundreds of thousands or millions of generally reddish, older stars. Whereas open clusters are found and made within the plane of our Galaxy, globular clusters form a halo around it and their creation is much less well understood.

In terms of observing, this all means that the majority of open clusters are found in or close to that misty river of stars stretching across the sky, the Milky Way, while globular clusters are seen all over the sky. When looking at them with the naked eye you'll see only fuzzy patches, but a pair of binoculars will reveal some truly spectacular gems.

What To See: Deep Sky

Outstanding Open Clusters

M45
Constellation: Taurus
RA 03h 45m 48s, dec. +24° 22' 00"
The Pleiades, or Seven Sisters, is one of the most splendid clusters in the night sky. With the naked eye, six stars of the cluster are easy to see, but counting up to 10 is possible. The cluster actually contains many hundreds of stars, and a decent pair of binoculars will be able to reveal many of them.

NGC 869 and NGC 884
Constellation: Perseus
RA 02h 19m 00s, dec. +57° 09' 00
This is the 'Sword Handle', a wondrous double cluster with two star clusters sitting side by side. They are both 0.5° in diameter and are easily visible to the unaided eye. Try sweeping the area with binoculars — the hundreds of stars, set against the backdrop of the Milky Way, make for a fine sight.

M7
Constellation: Scorpius
RA 17h 53m 54s, dec. -34° 49' 00"
Also known as the Ptolemy Cluster, this appears to be twice the size of the full Moon. To the eye, the 80 stars of the cluster appear as a bright clump in the Milky Way, but through binoculars the stars are resolved.

M35
Constellation: Gemini
RA 06h 08m 54s, dec. +24° 20' 00"
This cluster contains upwards of 200 stars and can just be seen with the unaided eye on good clear nights. Binoculars bring out the brightest 20 or so stars, while the rest form a diffuse oval wash behind.

M44
Constellation: Cancer
RA 08h 40m 06s, dec. +19° 59' 00"
Known as the Beehive Cluster, M44 contains hundreds of stars and can be seen as a misty patch with the naked eye. Binoculars are the best way to see M44: through them you'll see a dozen or so of its brightest stars.

Great Globulars

M13
Constellation: Hercules
RA 16h 41m 42s, dec. +36° 28' 00"
Known as the Great Globular Cluster, this is the best of its kind in the northern hemisphere. From a dark site, M13 can just be seen with the unaided eye, but its bright, round form is a stunning sight through a pair of binoculars.

M5
Constellation: Serpens
RA 15h 18m 36s, dec. +02° 05' 00"
This is thought to be one of the oldest of all globular clusters. It is easily found in binoculars and has a slightly oval-shaped appearance. What you'll see is a fuzzy blob, hinting at the vast number of stars it contains.

M22
Constellation: Sagittarius
RA 18h 36m 24s, dec. -23° 54' 00"
One of the brightest globular clusters, M22 is easily visible with the unaided eye, and a great sight through binoculars. It's larger than M13, which is impressive, but its place in the Milky Way's river of stars makes this a real jewel in the crown.

M3
Constellation: Canes Venatici
RA 13h 42m 12s, dec. +28° 23' 00"
This is another stunning globular cluster. It can just be seen with the unaided eye, but binoculars will reveal its bright, round shape that holds around 500,000 stars. 274 of these are known to be variable, the largest number in any known globular cluster.

M15
Constellation: Pegasus
RA 21h 30m 00s, dec. +12° 10' 00"
Looking like a slightly more compact M13, this densely packed object is an ideal target for binoculars. It appears as a round smudge with quite a compact central region, giving this distant star cluster a real sense of depth.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

These shining arks of stars come in all shapes and sizes, many the result of cosmic collisions

Andromeda Galaxy by Steve Peters

Galaxies are concentrations of millions or billions of stars, gravitationally bound together along with gas clouds and pockets of dust. There are probably over 100 billion of them in the Universe. Some of the largest nearby galaxies appear in the night sky as faint smudges of light, but it was only in the early 20th century that astronomer Edwin Hubble proved that they actually exist well beyond the Milky Way. Before then, they were thought to be spiral-shaped nebulae on the outskirts of our own Galaxy.

Hubble also established that galaxies vary in shape and size. Two-thirds have distinctive spiral patterns, while the rest range from neat ellipticals to irregular blobs. They can be dwarves containing millions of stars or giants harbouring trillions. Astronomers are still piecing together why this is the case, but collisions and mergers seem to be important in determining how a galaxy evolves. Central black holes also seem to govern how gas is consumed and when stars are formed within these cosmic conurbations.

Hidden Mass

Galaxies are much more massive than they look. Around 90 per cent of their mass is not in luminous stars and gas, but in unseen 'dark matter'. It's arranged in a spherical halo, which governs the motions of the stars within. This invisible cocoon explains why the outskirts of spiral galaxies spin faster than if they were influenced by the quantity of stars and gas alone. Dark matter also governs how galaxies clump together under gravity to form filaments and clusters. Yet dark matter remains an enigma, and astronomers are still trying to discern what it is. It must be exotic as it does not absorb or emit light.

Spiral galaxies such as the Milky Way are named for the arcs of bright stars that corkscrew into their centres. The spiral is a density wave embedded in a flattened disc of stars and gas that is arranged around a central bulge. Bright stars form where gas clouds are compressed. The disc is full of young stars and gas, and tends to be blue; the bulge appears redder. Discs form when a cloud of gas collapses under its own gravity, spinning faster as it shrinks vertically. Spirals are common across space, apart from in the centres of galaxy clusters, where discs are easily destroyed by collisions.

Shaped like rugby balls, elliptical galaxies are much like the bulges of spirals, but lack any disc. They contain little gas, and few stars are being formed within them. Old, red stars are the norm, travelling on inclined elliptical orbits. Groups of elliptical galaxies are often found in the centres of galaxy clusters.

Lenticular galaxies are lens shaped, their classification falling between spirals and ellipticals. Many are similar to spiral galaxies, containing a relatively small disc and large bulge, but lacking the spiral arms. These may be faded spirals, in which star formation has ceased. Others are likely to be the result of galaxy collisions, which could have ripped off part of a larger disc, or shut down star formation after a vigorous burst.

Irregular galaxies do not fall into any of the other main classification categories — they have no distinctive shape. This may be because they have been distorted in a collision or they may have formed that way. Some dwarf galaxies condensed in a haphazard manner from gas clouds and haven't settled into an ordered state.

What To See: Deep Sky — Glimpsing Galaxies

The Andromeda Galaxy, M31
Constellation: Andromeda
RA 00h 42m 42s, dec. +41° 16' 00"
The magnificent Andromeda Galaxy is the nearest large galaxy to the Milky Way, and it is possible to see it with the naked eye. Under dark, Moon-free skies, you should be able to find this spiral galaxy as a faint misty patch a short distance from the band of the Milky Way without optical aids. Using binoculars, you'll find it with little or no difficulty. It will be oval in appearance — although you won't be able to make out any of the individual stars within it. Through a 6-inch telescope the galaxy appears as a larger, elongated oval shape with a core that shows up as a slightly brighter area.

The Whirlpool Galaxy, M51
Constellation: Canes Venatici
RA 13h 30m 00s, dec. +47° 16' 00"
The Whirlpool Galaxy is a magnificent face-on spiral located in Canes Venatici. It can be found not far from mag. +1.9 Alkaid (Eta (—) Ursae Majoris). You'll need a large telescope to see its spiral arms clearly.

The Triangulum Galaxy, M33
Constellation: Triangulum
RA 01h 33m 54s, dec. +30° 39' 00"
M33 can just be seen with the naked eye under pristine dark skies, but light pollution means binoculars at least. It sits between mag. +2.2 Hamal (Alpha (a) Arietis) and mag. +2.1 Mirach (Beta (b) Andromedae).

The Sombrero Galaxy, M104
Constellation: Virgo
RA 12h 40m 00s, dec. -11° 37' 23"
Located just within Virgo, this spiral galaxy is easy to see in any scope. A 6-inch instrument shows an elongated glow, but its defining characteristic is a dark dust lane that cuts across the south of the central halo.

M81 and M82
Constellation: Ursa Major
RA 09h 55m 33s, dec. +69° 03' 55"
These galaxies in Ursa Major, M81 or Bode's Galaxy (co-ordinates above)and M82 the Cigar Galaxy, are close to each other in the sky, so we're treating them as one sight here. With a small telescope and a low magnification eyepiece, you'll be able to see them in the same field of view.

The Leo Triplet
Constellation: Leo
RA 11h 18m 55s, dec. +13° 05' 32"
The Leo Triplet is comprised of the spiral galaxies M65 (co-ordinates above), M66 and NGC 3628, and lies about halfway between mag. +3.3 Chertan (Theta (θ)Leonis) and mag. +6.6 Iota (ι) Leonis. Larger telescopes will show them clearly. Another group, M95 and M96, is nearby.

The Pinwheel Galaxy M101
Constellation: Ursa Major
RA 14h 03m 12s, dec. +54° 20' 57"
This face-on spiral galaxy is comparable in size to the Milky Way, and while it can be spotted in binoculars its magnitude of +7.9 means you'll need dark skies and a 6-inch telescope to see its spiral arms.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Whether they glow on their own or reflect the light of nearby stars, these clouds of gas and dust are popular targets

Flame Nebula by Doug Hubbell

Nebulae are clouds of gas and dust that are scattered throughout the Milky Way, mainly in the galactic disc, and it's here that stars are born. The word is Latin for 'little mists' — long ago, we considered all deep-sky objects to be nebulae, galaxies included, because they were faint fuzzy patches in the otherwise black night. These days, not only can we differentiate between nebulae and galaxies, but we know that several types of nebula exist.

The most famous nebula of them all, M42 in Orion, is what's known as an emission nebula. Nebulae of this type have a glow of their own, a result of stars within or nearby ionizing the gas cloud. On the other hand reflection nebulae, like the one around the Pleiades star cluster in Taurus, are only visible because there are some stars nearby that light up the gas and dust, just as the Sun lights up a cloud in an otherwise blue sky.

Dark nebulae, such as the Horsehead Nebula, don't glow at all, as they are so dense they absorb light. They are only visible because they are in front of a bright nebula or field of stars. We effectively see a silhouette of the cloud, but no detail in it.

You might think that planetary nebulae, such as the Ring Nebula in Lyra, have something to do with planets, but you'd be wrong. They get their name because, through a telescope, many have the appearance of a faint, small, fuzzy disc and can look a lot like a planet. These nebulae are formed during the death of a star of similar mass to the Sun. As it grows unstable, the star puffs off its gaseous atmosphere to form clouds around it. Stars larger than the Sun end their days explosively in a supernova, leaving a spectacular remnant in their wake.

Astro images will reveal that many nebulae have vivid colors — typically red in emission nebulae from ionized hydrogen atoms and hues of blue stars in reflection nebulae — but the view through binoculars or a telescope will be quite different. Visually, nebulae appear in shades of grey.

Stellar Nurseries

Nebulae are where stars are created. One idea of how it all starts is that a shockwave from a nearby supernova explosion compresses the cloud. Once the density of the gas passes a critical point, gravity takes over. Gravity causes clumps of the nebula to pull together. The pressure at the center of the clumps builds and the temperature rises dramatically. If there is enough gas to fuel the process, the region can become a protostar. If the temperature in the clump reaches 10 million degrees Celsius, the nuclear furnace that powers stars ignites. Over tens of millions of years it settles into normal life and joins what's called the main sequence, like our own Sun.

What To See: Deep Sky — Amazing Nebulae

The Orion Nebula, M42
Constellation: Orion
RA 05h 35m 17s, dec. -05° 23' 28"
M42 is the brightest nebula in the night sky and the only one that can be seen with the naked eye. With a casual glance below the three belt stars of Orion in a dark, light-pollution free sky, you'll see this emission nebula as a small misty smudge. A pair of binoculars will begin to reveal its curving shape. With a small telescope, you will start to see some structure. In the heart of the Orion Nebula are four stars. These are part of the Trapezium open cluster, named because of the shape the four stars form. It's the radiation from these stars that is energizing the entire nebula and causing it to glow.

The Crab Nebula, M1
Constellation: Taurus
RA 05h 34m 32s, dec. +22° 00' 52"
M1 is what remains of a cataclysmic stellar explosion witnessed from Earth in 1054. It can be spotted with a small telescope, but it's best seen through a really large aperture instrument — only then does its texture start to emerge.

The Lagoon Nebula, M8
Constellation: Sagittarius
RA 18h 03m 37s, dec. -24° 23' 12"
This easily noticeable emission nebula can be seen as a brighter patch with the beginnings of a core in 10x50 binoculars, even sitting where it does within the constellation of Sagittarius — a busy and star-rich area of the Milky Way.

The North America Nebula, NGC 7000
Constellation: Cygnus
RA 20h 59m 17s, dec. +44° 31' 44"
It takes a bit of practice to see emission nebula NGC 7000, also known as the North America Nebula, as it's such a large object. It's close to the bright star Deneb in Cygnus, and the surrounding area contains many targets for binoculars.

The Omega Nebula, M17
Constellation: Sagittarius
RA 18h 20m 26s, dec. -16° 10' 36"
This glowing emission nebula and star-forming region sits among the star fields of Sagittarius. It has a curved shape that can be likened to the Greek capital letter omega, Ω, hence its name, though it is sometimes called the Swan Nebula.

The Dumbbell Nebula, M27
Constellation: Vulpecula
RA 19h 59m 36s, dec. +22° 43' 16"
This fascinating and relatively bright planetary nebula appears as a misty oval in small telescope, with the Milky Way providing a marvelous backdrop. The 'dumbbell' shape only becomes apparent through large instruments.

The Horsehead Nebula, Barnard 33
Constellation: Orion
RA 5h 40m 59s, dec. -02° 27' 30"
The Horsehead Nebula, to the south of Orion's Belt in the Orion Molecular Cloud Complex, is a dark nebula that appears silhouetted against a brighter background of nebulosity. You will need a large aperture instrument and dark skies to make it out.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Not only does the Red Planet have seasons just like ours, they're also easy to see, writes Paul Abel

Mars by Jimmy E.

The changing of the seasons here on Earth can be quite spectacular. In many regions the whole landscape is transformed by the onset of spring: as the cold winter snows retreat and the days become longer, trees come into blossom and hibernating animals awaken. The people of ancient civilisations were particularly keen observers of these cycles, since their existence depended upon knowing when to plant seeds and harvest crops. It is no wonder that they constructed huge monuments to mark important dates like the spring equinox.

The well-defined seasons of winter, spring summer and autumn are the result of the Earth's 23.5° axial tilt. If the northern hemisphere is tilted towards the Sun it experiences summer, while the southern hemisphere experiences winter. Over the course of a year, both hemispheres experience all of the seasons, although because Earth's orbit is slightly elliptical they are not of equal length — summer in the northern hemisphere is longer than it is in the south.

Seasonal Similarity

Earth is not alone in having an axial tilt — all of the planets do, from Mercury's fractional 0.03° to Uranus' massive 82.2°. But Mars' tilt is the closest to Earth's at 25.2° and as such it experiences similar seasons — although being farther from the Sun means they last for longer.

Consequently, Mars is a very dynamic world, where the changing of the seasons can produce dramatic, planet-wide changes that are visible in small telescopes.

Mars has been closely scrutinised by Earthbound astronomers from the middle of the 19th century onwards, and although our early ideas about Martian seasonal changes being due to vegetation were wrong, the fundamental idea that its seasons have a lasting effect on its features is correct. All you need to do to see just how much Mars' surface has changed is compare a map of Mars from the 1950s to a current one.

In order to keep track of seasonal changes, we need to devise a calendar for Mars. Astronomers use a quantity called Martian solar longitude, or 'Ls', which is measured in degrees. Mars' orbit is divided into 12 months represented by 30° segments. For Mars' northern hemisphere, 0-90°° is spring time, 90-180° is summer, 180-270° is autumn and 270-360° is winter. Just like Earth, the Martian hemispheres experience opposite seasons, so if it is spring in the northern hemisphere it will be autumn in the south.

Month by Month

By the end of May, Mars will be a reasonably large 18 arcseconds, and its northern hemisphere will be slightly tilted towards us. By the time of opposition, Martian solar longitude has a value of 157°, so it is will be early summer in the north. You can look up the value of Ls in the freeware program WinJupos (www.grischa-hahn.homepage.t-online.de).

The large northern polar ice cap will now have shrunk dramatically, appearing as a small white patch in the far north. As the cap recedes, a dark band can usually be made out surrounding it. This is the Lowell band, which can sometimes be very prominent and appears a dark brown in color. With a 6-inch or larger telescope you may also be able to see an equatorial cloud band, which can give the northern part of Syrtis Major a distinctly bluish cast.

The melting of the north polar cap returns a lot of volatiles into the Martian atmosphere, and over the following months you should keep a look out for bright white clouds and fog patches. There are a number of well known places where they form: the Hellas, Argyre and Chryse basins for example. Sometimes they form around the vast shield volcano Olympus Mons or the other volcanoes in the Tharsis Plateau. Clouds and fogs sometimes encroach into the darker albedo features; you can enhance their contrast using a blue filter such as a Wratten number 80 (W80). If they form on the sunward limb, you can watch them dissipate as Mars rotates and the late morning Sun disperses them.

By the end of July, solar longitude on Mars will be 195°. Summer will have now given way to autumn and it will be slowly getting colder in the north. However, spring will have arrived in the south and the southern ice cap will now start retreating, and by the start of August the dust storm season will be underway. This is the time to keep a look out for storms which usually start off as small orange clouds. They may remain small or they can continue to develop until they have encompassed the entire globe, hiding all but the most prominent features.

By October, the southern hemisphere will be tilted towards us. It will be spring in the south, and if you have access to an 8-inch telescope you should be able to follow the shrinking of the south polar cap over the next couple of months. By the end of November, Martian solar longitude will be 271°, marking summer solstice for the southern hemisphere. The Martian disc will now be small, but imagers with large telescopes should still be able to pick out any dust storms.

Mars' Shifting Ice Caps

The extent of Mars' frozen poles varies greatly with the seasons.

The polar ice caps of Mars can be very striking and can be glimpsed in a 4-inch telescope when prominent. The caps wax and wane with the planet's seasons. At the time of opposition, it will be summer in the north, and so the northern ice cap will have shrunk to a small white patch, and it will probably be quite difficult to see.

As we move into September, Mars' southern hemisphere will start to tilt towards us. It will be spring in the south, and from the end of October onwards you should be able to watch the large south polar cap start to shrink. A blue Wratten 80 filter will help enhance the polar regions. By December, Mars will be quite small, and so you'll need at least an 8-inch telescope and a magnification of 250x or more to see the south polar cap.

Dust in the Wind

Tiny dust storms can develop into planet-wide events.

Although the Martian atmosphere is not very substantial, it can still produce winds that can develop into dust storms. The storms begin as small orange clouds, and can grow quite rapidly. There are three categories:

1. Local: Small yellow-orange clouds usually less than 2,000km in size, but can encompass whole regions (such as the Hellas basin).
2. Regional: These are much larger and may affect a whole hemisphere.
3. Global: These cover the entire planet, and may hide the surface features for many months at a time.

In 2001, a dust storm was observed in the Hellas basin and developed into a global event shortly after. Another famous global dust storm occurred in 1971, obscuring the entire planet just as the Mariner 9 spacecraft arrived.

Dust storm season usually starts at a Martian solar longitude of 180°, so for this apparition the season starts in early July and will continue for the rest of the year. Small yellow clouds show up well in a red Wratten 25 filter, while a green filter can help to enhance larger storms.

A Martian Calendar

The 12 months of Mars, and some events to expect in them:

About The Writer
Dr. Paul Abel is an astronomer at the University of Leicester. Listen to him on BBC Sky at Night magazine's Virtual Planetarium.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

How a view through a telescope as a boy kindled a life-long love of our planet's only natural satellite.

Mare Nectaris, Fracostorius and Piccolomini by Ronald Piacenti Jr.

I had my first telescopic view of the Moon when I was seven years old. A family friend, Major AE Levin, had his observatory in Selsey and I went there (long before I came to live there myself) to use his 6-inch refractor. The Moon was our first target; I looked through the eyepiece and saw the mountains, the craters and the valleys, obviously without understanding what they really were. I was fascinated, and I remember saying, "When I grow up I'm going to study the Moon." I did.

Of course, things were different in 1930. We knew much less about the Moon than we do now; it was thought that the atmosphere might be substantial enough for thin clouds to form and that a certain amount of volcanic activity might linger on. Our ignorance was complete about the far side, which is always turned away from Earth. As for travel there — well, even after the end of the Second World War, one very senior astronomer, Richard van der Riet Woolley, made the categorical pronouncement that the whole idea of space travel was "utter bilge".

So to me, as a boy, the Moon seemed to be far out of reach. All the same, I wanted to find my way around. So when I acquired my 3-inch refractor in 1933, I set about it. That telescope cost £7.10/-. I saved up for it and it remains one of my treasured possessions.

My observing and recording method worked for me, and I believe it will also work for other newcomers, so it seems worth passing on.

Lunar formations seem to alter in appearance according to the changing angle of solar illumination, and this can be really confusing. The large walled plain Maginus provides a good example of this. When seen near the terminator it is imposing, with peaks in its wall casting long shadows across its floor, but under high illumination it is difficult to identify at all. It was once said that "the full Moon knows no Maginus". Some craters with very dark floors (Plato, Billy, Grimaldi) or very bright walls (Aristarchus, Proclus) can be located whenever they are sunlit, but are exceptions rather than the rule.

What I did was take an outline map and make a pious resolve to make three drawings of every named object under different lighting conditions. The whole project took me over a year. I still have those sketches. Scientifically, of course, they are of no value, but when I finished the project I could find my way around the Moon more easily than I could my then home town of East Grinstead.

One lesson I learned during this project: don't try to draw too large an area at the same time; concentrate upon one thing. For example, the great dark-floored crater Plato is 109km in diameter. When drawing it, make it at least an inch across. Do the main outline first, then change to a higher magnification and fill in the fine details.

A new mare?

Today, a telescope such as my 15-inch reflector can be used to take photographs of the Moon far better than any professional observatory could have managed only a few decades ago. CCDs and similar devices have revolutionised everything. I didn't have CCDs, and depended on my eyes alone. But it was then possible for the amateur to make interesting discoveries and I thought I'd made two, though for one of them I later found out that I was 30 years too late.

When I finally took off my RAF uniform in 1945, I returned to the Moon. I was lucky enough to be given access to really large refractors, notably the 33-inch at Paris, the 27-inch at Johannesburg and the Lowell 24-inch at Flagstaff in Arizona, but I still used the modest reflectors in my own observatory at East Grinstead (it was 1967 before I settled down at Selsey). I concentrated on the formations right on the Moon's limb, which are very foreshortened and are carried in and out of view depending on the libration.

In the late 1940s I drew what seemed to be the edge of a mare, most of which was on the far side so that I could only see a tiny part of it — and then only under extreme libration. It wasn't on the maps I had. I called it Mare Orientalis, the 'Eastern Sea', and sent my results to the British Astronomical Association's Lunar Section. I was convinced that I was the first to see it. But ... I wasn't. It is clearly shown in the map produced in 1906 by the German astronomer Julius Franz — who also called it the Eastern Sea (because it lay at the eastern limb; much later the International Astronomical Union reversed east and west). Of course, we now have detailed maps of the far side, and know that the Mare Orientale is a vast ringed structure, unlike anything else on the Moon. At about the same time, I drew the large limb crater now named Einstein. I think I was probably the first to see this. Not that it matters!

An enduring fascination

At least my maps of the libration areas were used. The Russians asked me for them, and of course I sent them — they made me an honorary member of the USSR scientific society, and invited me to Moscow, despite the Cold War. I was an insignificant member of a very large team, but it was an exciting period, followed by the lunar landings. I was doing the TV commentaries during the Apollo missions; I was on the air when Apollo 8 carried men round the Moon for the first time. I was also broadcasting when Neil Armstrong made his "one small step" onto the barren rocks of the Sea of Tranquility. I can't remember my exact words, and unfortunately the BBC have lost all the tapes, but it was a moment never to be forgotten.

After Apollo, I concentrated my Moon observations on TLP, or transient lunar phenomena (a term I believe I invented). Much work remains to be done here, and there is no doubt that TLP are real; the Moon is not totally inert, though major upheavals belong to the remote past. The next stage will be the setting up of lunar bases, and the Moon will at last become a living world.

At the age of 86, I cannot hope to see this, or to carry out much more observation, but my interest and enthusiasm are as great as ever. A Moon man I've always been; a Moon man I'll remain to the end of my days.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Whether you have a phone camera or a pro camera, we show you how to take your first lunar astrophoto.

Crater Copernicus by Bob S.

The silvery Moon riding high in the sky on a crisp winter's night is a perennially alluring sight, and for the photographers among us its smooth seas, mountains and crater-flecked plains present a similarly inescapable attraction. For those just starting out in astrophotography, the Moon's brightness and large apparent diameter make it a superb target to cut your astro imaging teeth on. Indeed, nowadays you need little more than a smartphone camera and small telescope to snap detailed images of our satellite's spectacular, rugged surface.

Here, we're going to explore some of the basics of lunar imaging, from the techniques that can produce great results to the features and phenomena that make ideal subjects for beginner shots. We'll also use key astro imaging skills — such as composition and tracking a target — in two step-by-step projects.

Afocal Imaging

Capturing the view through your telescope with a smartphone.

If you own a small scope then you may have already tried one of the simplest methods for grabbing a picture of the Moon: afocal imaging. This is a fancy name for something that's really very simple - holding your camera up to the eyepiece of the telescope and snapping the view.

Traditionally, point-and-shoot cameras and the like have been used for afocal imaging with great success, but now - in the age of the camera-equipped smartphone - wonderfully detailed, sharp images can be captured with just the mobile in your pocket. One of the main challenges of afocal imaging is keeping the camera aligned with the eyepiece so that the Moon stays in view. Special adaptors are available to buy that will hold a smartphone or digital camera in place to make this easier, but if you're going the handheld route then we recommend using a low power eyepiece at first.

Basics of High Frame Rate Imaging

Learn how to cut through the wobbles of our atmosphere to create sharp lunar images.

Hold a digital camera or smartphone up to the eyepiece of a telescope and snap the Moon's disc afocally and you're likely to notice that from shot to shot the sharpness in the image varies. In one area of an image you might capture a crisp view of a crater field, whereas elsewhere in the shot the image is slightly blurry. In the next shot another area may be sharper or the whole disc may be noticeably soft.

This variation in detail from moment to moment is all down to the turbulent undulations of the atmosphere high above us. When astronomers talk of good 'seeing' conditions, what they mean is that these undulations are less pronounced and the view is steadier. But even on a 'normal' night there may be very brief moments of steadiness that provide a fleeting, sharp, view of the lunar surface. What if there were some way we could capture these transient moments and combine them all into one really sharp image?

This is precisely the principle behind high frame rate lunar imaging. By using a webcam or a specialist high frame rate camera and a computer, astrophotographers can capture a short video of hundreds, perhaps even thousands, of individual frames. Then, using software such as RegiStax (www.astronomie.be/RegiStax) or AutoStakkert (www.autostakkert.com), the frames from these videos can be sorted and only the best selected. These are then stacked together to form a final image that is carefully sharpened to produce a shot that's beautifully detailed.

Focal Length and Composition

Learning how to place your target properly within the image frame will improve your astrophotos.

When it comes to composition, the choice of what focal length to image the Moon at naturally makes a tremendous impact on the final picture.

A short focal length DSLR lens will produce a wide view, with the Moon appearing tiny - perfect for conveying a sense of the great expanse of surrounding sky or incorporating a large-scale atmospheric phenomenon.

Using a longer focal length lens, or small refractor, will change the feel of the image entirely: here faraway trees, hills or buildings can be brought right up close with the disc of the Moon looming over them. And then there's the high-magnification world of high frame rate imaging, where the field of view is generally very small. Even here it's worth considering where in the shot to place the surface feature you're imaging, and whether a carefully planned mosaic could draw the viewer's eye more effectively.

Step-by-Step: Capture the Full Moon as it Rises

Image the full Moon rise with a DSLR or bridge camera, a lens or small refractor, and a static tripod.

1. Choose your location
An interesting foreground makes for an attractive moonrise shot. A sea horizon offers a dramatic setting if you're planning to use a longer lens, especially with the atmosphere distorting and reddening the Moon's disc. Alternatively a high vantage point can give a great sense of depth and distance.

2. Timing and direction
The time the Moon rises and the direction it does so are also vital considerations. Planetarium software such as Stellarium (www.stellarium.org) and smartphone apps such as The Photographer's Ephemeris can be extremely useful for planning precisely where you need to be looking and when.

3. Set up your equipment
Set up 10-15 minutes before moonrise, just in case you have kit issues that need addressing. If you're at a new site, this will also give you a chance to choose the best view or foreground for the photo. You'll typically only have a short window to get the shot once the Moon is above the horizon, so preparation is crucial.

4. Compose the shot
Think about the composition of your shot. You may have decided on your foreground, but how do you want to include it? With a plain horizon you could offset the Moon, perhaps to include a feature of the landscape. If you have a sea horizon, the moonlight on the water might help create an attractive focal point.

5. Capture the shot
Once the Moon's up, experiment with the exposure and ISO settings to ensure you get detail in your foreground without overexposing the Moon. It's all about waiting for that ideal moment when the Moon's light is balanced with the fading twilight, the clarity of the sky and how high the lunar disc is above the foreground.

6. Edit and enhance
When you've captured your shots, it's worth loading them into photo editing software for final enhancements. Of particular use for moonrise images are the tools that allow you to lighten the 'shadows' or darker regions within an image - this can really help to bring out foreground detail that is slightly underexposed.

Step-by-Step: Imaging Earthshine

Discover how to image the portion of the Moon that's illuminated by the light scattered off Earth.

1. Consult a calendar
Find out when the Moon will be a thin crescent - there's a phase chart in every BBC Sky at Night Magazine, and you can also use smartphone apps or planetarium software such as Stellarium (www.stellarium.org). The four days either side of new Moon are ideal.

2. Get your kit set up
Depending on when you're imaging, the Moon will be relatively low in either the west or east, so ensure you have a clear view. Set up your mount, scope and camera as normal — you'll need a driven mount. We'll be using a DSLR and small refractor or long lens for this tutorial.

3. Bring the Moon into view
Once set up, move or slew your telescope to bring the Moon into the field of view. If your mount can track at the lunar rate, as opposed to the sidereal one, it's a good idea to select that now, especially if you intend to use a longer focal length lens or scope.

4. Focus the image
Getting a sharp image is the key to capturing a great earthshine shot, so confirm that the view is in focus. Here the live preview function on modern DSLRs is particularly helpful. Observing the ragged inner edge of the lunar crescent is a good way to judge the focus.

5. Finalize composition
Next look at the composition of your shot. If your field of view is fairly wide think about including some trees, a distant hedgerow or some buildings. If you're shooting close in, consider how the heavily overexposed crescent and the glow around it will look in the frame.

6. Capture
Be sure to shoot in RAW to give you greater flexibility when it comes to editing. Unlike other forms of lunar photography, earthshine generally requires only single shots. Using a remote shutter release cable will keep the image free from blurring caused by shake introduced when you push the shutter button.

7. Settings
The camera settings required will vary between equipment setups. Exposures of a few seconds at ISO 400-1600 should work, with the lunar crescent being overexposed by necessity. Longer, low ISO exposures, for example, will produce smoother images but may cause foreground blurring as the mount tracks.

8. Tweaks, crops and final edits
Editing programs like Photoshop (paid) and GIMP (www.gimp.org) allow you to tweak the 'Levels' to improve the colour balance, brightness and contrast. You may also like to employ the 'Unsharp Mask' tool to sharpen up fine detail on the lunar disc.

Top Lunar Surface Targets

If you want to try out high-magnification lunar imaging, here are eight top targets to get you going.

Catharina, Cyrillus and Theophilus
These three craters are some of the most photographed on the Moon. For a particularly dramatic shot, image them two days before first quarter.

Aristoteles
Crater Aristoteles sits on the edge of the Mare Frigoris. Its intricate ejecta blanket and terraced walls make it a wonderful crater to image when it is being lit from a low angle.

Gassendi
You'll find Gassendi on the northern shore of the Mare Humorum. When it comes to imaging it, good seeing conditions are needed to clearly reveal the interesting rille system within.

Plato and the Vallis Alpes
The region on the northeastern edge of the Mare Imbrium is rich in attractive targets and the crater Plato and the nearby Vallis Alpes are two that no lunar imager should overlook.

Rupes Recta
Also known as the Straight Wall, this huge fault is a fascinating feature to observe and image. You'll need to catch it when it's illuminated obliquely however, otherwise it's practically invisible.

Schröter's Valley
Vallis Schröteri, or Schröter's Valley, sits next to the prominent crater Aristarchus. Capturing the fine detail of this winding volcanic feature is a good test of a beginner's imaging skills.

Tycho's Ray System
The bright material — known as a ray ejecta — blasted across the Moon's surface by the impact that formed the crater Tycho is one of the few lunar features which is best seen at full Moon.

Copernicus
One of the most spectacular craters on the Moon, Copernicus has it all. Its grand terraced walls, prominent central peaks and surrounding ejecta blanket make it a great imaging target.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Paul Abel's guide to the closer planets shows how to get the best views and sketch the results.

Jupiter by Mark Bell

There was a time before webcams and CCDs when photographic film had a resolution lower than that of the human eye. During this era, the only reliable tools astronomers could rely upon were their own vision and a pencil, but even with these limited resources some startling discoveries were made. The astronomers of this era seem to be like great explorers venturing out into a vast and complex cosmos, their drawings and observations rather like postcards from alien frontiers.

Today, the sensitivity and size of imaging equipment has improved immeasurably. Yet even in the 21st century, there are still areas of amateur astronomy in which visual observers can make valuable contributions. Visual observers need many specialist techniques to obtain reliable results that can go into the scientific record and here we introduce some of these observing skills with the aim of making you a better astronomer. We're going to look at the most rewarding planets for study: Venus, Mars, Jupiter and Saturn.

Venus

Venus can be a challenging object for visual observers, yet in the 1960s it was such astronomers who helped to establish that the planet's clouds have a three-day rotation period. With Venus, a visual observer's main objectives are to obtain disc drawings that correctly show the phase and to record elusive cloud markings.

A cursory telescopic view of Venus will reveal a bright white disc with a phase. The bright cusp caps covering the poles may be glimpsed, but that will probably be the only detail. Don't be put off, though: with time and patience subtle cloud markings come into view. The first thing to do is to find the correct magnification: one that gives a reasonable disc size and is suitable for the seeing conditions. I find 130-160x to be about right. Venus is also best observed in bright skies, as this reduces the glare from the disc.

As with all planets, don't expect to see all the fine details at once — you will need to engage with your visual system (one of the most remarkable adaptive optics kits on Earth). Ask yourself what you can see on the disc and slowly your eyes will respond. Spend about 15 minutes looking at the planet's disc before you start drawing.

To sketch Venus you'll need a circle 50mm in diameter. Draw in the phase and then, with a 2B pencil, gently shade in the subtle cloud markings. Eyepiece filters are a great help as they allow you to see into different depths of the atmosphere. Red and blue filters help to enhance cloud markings, while a yellow filter will bring out the polar collars.

The Schröter Effect
Look at Venus when it's predicted to be at half phase and you'll notice that the phase is actually slightly less than half. This is the Schröter effect, where Venus's observed phase is always less than the theoretical one, and it is particularly prominent in a blue filter.

The phenomenon was first recorded by Johann Schröter in the 1790s, and is due to light being scattered in the thick Venusian atmosphere. You can record it for yourself: on your drawing: simply measure the distance (in mm) with a ruler from the limb to the terminator and divide this distance by 50 to get the observed phase of Venus. Do this for all of your drawings and you can plot the decreasing phase against time on a graph and show how the effect changes over the course of an elongation.

Mars

The ochre disc of Mars is full of subtle, slowly changing features. Mars is a world of vast volcanoes, continent-sized canyons and majestic deserts. It's not uncommon for fogs to collect in the basins such as Hellas and Argyre, and the volcanoes attract brilliant clouds at their summits. Martian meteorology changes over the course of a few hours, and it can all be recorded and studied visually.

The well-defined Martian seasons produce different phenomena. During the apparition of 2013-14, it was springtime in the northern hemisphere, and the brilliant north polar cap shrank dramatically as it sublimated away. Recording the retreat and advance of the polar caps is important as it reveals information about the Martian climate.

The dust-storm season occurs during spring and summer in the southern hemisphere. Telescopically, these storms resemble small orange clouds, and they can engulf the entire planet. It may take many months for the dust to clear and afterwards there may be changes to the dark albedo features. You can track the progress of large dust storms, recording their size and changes to local surroundings. A green filter helps enhance them.

Mars tolerates high magnification well because red light is less affected by Earth's turbulent atmosphere. At powers of 300x, dark albedo features like the Syrtis Major will show a multitude of subtle structure.

Drawing Mars requires some patience. You can't spend any longer than 15 minutes doing so as Mars's rotation will have moved the features away from where you've placed them in the drawing. Sketch the phase first if it is present, then the polar caps. Spend seven minutes putting down the obvious features and use the remaining time to put in any bright clouds you can see. A blue Wratten No. 80A filter helps enhance white clouds. Aim to make two to three drawings over a night to show how the clouds change.

Jupiter

The restless clouds of Jupiter have generated plenty of work for visual observers for hundreds of years. Through a telescope, this gas giant is differentiated into darker belts and brighter zones. Powerful jet streams carry large storms along, presenting us with an ever-changing cloudscape.

Jupiter has a large disc and magnifications of 160x or more are sufficient to reveal a lot of fine detail. A red filter helps to enhance bluer features like festoons along the equator. Conversely a blue filter helps to enhance redder objects like the belts and the Great Red Spot. A yellow filter gives good all-round contrast.

It takes practice to record Jupiter correctly, but doing so will really hone your observational skills. A Jupiter drawing requires the correct blank: this planet is appreciably flattened due to its rapid rotation, so the standard blank is 64mm wide but only 60mm high.

Like Mars, Jupiter rotates quickly; in this case you have 10 minutes to make your sketch. First draw the main belts and large storms, recording the ones near the preceding edge first as these will vanish soonest. Spend the remaining time adding in the finer details.

Supermoon
Jupiter's most famous and persistent storm is the Great Red Spot, a vast hurricane situated in Jupiter's South Tropical Zone. Visible to a 5-inch scope, the Great Red Spot drifts in longitude at varying speeds; this drift rate can be measured.

When the storm is visible, watch as it moves towards the central meridian. When you think its centre is on the meridian, record the time. Use freeware software WinJUPOS to convert the time into longitude and repeat this whenever you observe the Great Red Spot. You can plot the resulting longitudes against time and look at how quickly the spot is moving in Jupiter's atmosphere.

Saturn

It is often said that majestic Saturn is a 'quieter' Jupiter. The belts and zones of Saturn's atmosphere are less well defined, but the storms that this planet can produce are even more ferocious.

Watching and charting storm activity is one of the main tasks for visual observers of Saturn. Storms are seasonal, occurring every 30 years, and usually take the form of a large white oval on Saturn's equator. The next outbreak is due near 2020.

Recently Saturn has produced other storms: quite unexpectedly in late 2010 a large storm erupted in the planet's northern hemisphere, lasting into 2011. This powerful storm churned up the North Tropical Zone, reminding us of the need for a constant vigil if we're to catch the next outbreak.

To really view Saturn, you'll need to use a power of 160x or more; 250x is a good all-round magnification. Drawing Saturn requires five accurately placed ellipses — so don't try to do it free-hand, use a carefully produced blank.

Saturn is also a quick spinner, so spend about eight minutes drawing in the main features on the disc and the rings, and use the final four minutes to finish the fine details such as the fainter belts and shadows. Filters work well for Saturn: yellow enhances the contrast between belts and zones, while light blue helps to emphasise redder features. Also watch out for a bi-coloured aspect of Saturn's rings: occasionally Saturn's outermost ring, the A-Ring, appears brighter in a blue filter than in a red one. Although rare, this phenomenon has been reported by visual observers and is worth keeping an eye out for.

Keeping a Log Book

Keeping a log book is an essential skill for any visual observer. It will keep your observations in a logical structure and you'll be able to look back and see how your drawing skills have developed. Your log book should be a sturdy bound notebook, and every observation should include the following information:

• The Date of Observation
• The Time, always in UT
• The Telescope and Magnification, along with the details of any filters used
• The Seeing Conditions, recorded using the Antoniadi scale, which runs in Roman numberals from I to V; I is perfect seeing and V is a very poor unfocused image

Tools of the Trade

Eyepieces
A selection of medium- and high-power eyepieces, giving a range of magnifications to suit your seeing conditions. A useful range is 160-190x for low power, 200-250x for medium power and 300x-plus for high power.

Filters
These help to enhance different features on planetary discs. Red, blue and yellow filters are invaluable.

Pencils
Some planetary features are more subtle than others, so you'll need a range of pencils from HB to 6B to capture as many as possible.

Red Light
White light destroys night vision, so always use a red light to draw.

WINJUPOS
This essential free software displays the features present on Jupiter or Saturn's disc at any date and time, and gives you the planetary longitudes for both gas giants so you can record the location of details. It is especially helpful as these planets have three systems of longitude due to their different bands of rotation.

About The Writer
Dr. Paul Abel is an astronomer based at the University of Leicester. You can listen to him on the BBC Sky at Night Magazine Virtual Planetarium each month.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Explore the seas and craters that texture the lunar surface with our beginners' observing guide.

Sea of Serenity by Craig Heaton

The Moon is an ideal object to begin your observing odyssey because it is big, bright and covered with amazing detail. But the thing that surprises most novice observers is the variation it holds. Though the same hemisphere faces Earth at all times, what you can see on the Moon changes from one night to the next.

You may be forgiven for thinking that full Moon is the best time to examine our close companion — not so. While this is a good time to see the long, bright rays of ejecta surrounding prominent craters such as Tycho, the high altitude of the Sun in the lunar sky means no shadows are cast, resulting in a washed-out view of the Moon.

In general, the best time to view a given lunar feature is when the terminator, the demarcating line that separates lunar day and night, is nearby. This is the region where the Sun is either rising or setting, where crater rims and mountain peaks stand out in stark relief, casting inky black shadows across the lunar surface that exaggerate their presence. Those further from the terminator show hardly any shadows and are harder to make out.

At day zero of the lunar cycle — new Moon — the whole of the dark lunar hemisphere points towards Earth. Over the next 15 days the terminator slowly creeps across the lunar surface from east to west until the disc is fully illuminated at full Moon. Then the tables are reversed as the encroaching darkened hemisphere heads west with each passing day, until the diminishing crescent becomes lost in the pre-dawn twilight.

Peering Beyond the Limb
The nature of the Moon's orbit generates another effect that is a boon to lunar observers, a rocking and rolling motion that we call libration. The Moon's orbit is elliptical, and as a result its distance from Earth does not remain constant. When closest it speeds up slightly; when more distant it slows down. This small variation is enough to cause the Moon to 'nod' back and forth on its axis, giving us an occasional chance to see a little more around its eastern and western edges.

The orbit is also slightly inclined, and this causes it to sometimes appear above the Earth's orbital plane and sometimes below. This gives us an opportunity to peek over the top, and under the bottom, of the Moon over time. Taken together, this libration allows us to see a total of 59 percent of the Moon's globe, revealing tantalising features normally hidden from view.

With the naked eye it's easy to see the progression of lunar phases, full disc effects such as earthshine and the major lunar seas. Binoculars increase the detail you'll see: as well as dark seas, you'll now be able to spot individual craters and large mountain ranges, especially when they are close to the terminator. The smallest craters you'll be able to pick out will depend on how still you can hold your binoculars, but a pair of 7x50s should comfortably reveal features down to about 50km across.

A telescopic view of the Moon is amazing and one that never gets old. At low magnifications, the amount of detail visible is breath-taking, especially close to the terminator where relief shadows really help to emphasise the detail. Upping magnification by using shorter focal length eyepieces will get you in closer and give you opportunity to 'roam' around the lunar landscape.

Trifles and Troubles
The view you have of the Moon through a telescope will differ from what you see with the naked eye or binoculars depending on its optical arrangement. Through a refractor or compound instrument, the Moon will appear flipped west to east, while through a reflector the image will be inverted.

If you look at the Moon with a telescope you may also notice the surface appears to gently wobble or sometimes even shimmer. This effect is caused by air moving through the atmosphere of our planet, and the greater the turbulence the worse the views.

Such 'seeing' conditions can vary from minute to minute and night to night. The best views will always be had when the seeing is steady and these undulations are less intense; poor seeing, on the other hand, results in loss of detail and fuzzy lunar features.

For centuries, telescopic observers have also reported seeing short-lived changes in brightness on the surface of Moon, events that are collectively referred to as transient lunar phenomena, or TLPs. They have been described as luminous spots that suddenly appear and vanish, localised patches of colour and temporary blurring or misting of the Moon's fine surface detail. However, despite several high-profile reports — including those from Sir William Herschel in 1787 and French astronomer Audoiun Dollfus in 1992 — their existence remains debated to this day.

The problem is that TLPs, being transient by nature, are hard to independently verify and impossible to reproduce. Most are spotted by lone observers, or are only witnessed from a single location on Earth, casting doubt on whether they truly occurred at all. Some believe that TLPs are little more than the result of poor observing conditions or equipment issues. Assuming they do occur, the most popular theory to explain them is residual outgassing from below the lunar crust.

What does seem clear is that TLPs, whether real or imagined, are more prone to occur on some areas of the lunar surface than others, with more than one-third of official reports coming from the region around the Aristarchus plateau.

The Many Guises of the Moon
Even to the naked eye, our satellite is a beguiling subject.

Earthshine
The Moon is not solely lit by sunlight. When it is in a slender crescent phase in the evening or dawn twilight, it's sometimes possible to see its dark portion gently glowing due to sunlight reflected off the oceans and clouds of planet Earth. This effect is known as earthshine. Our planet actually reflects more light onto the lunar surface than the Moon gives us when it is full.

Lunar Halos
On frosty nights, often when the Moon is or near full, you may be able to spot a faint ring of light caused by ice crystals refracting the moonlight in the upper atmosphere. Since the ice crystals are normally all hexagonal, the ring is almost always the same size; it has a diameter of 22°. Sometimes it is also possible to detect a second ring, 44° in diameter.

Red Moon
There are two reasons the lunar disc may take on a ruddy hue. The first is if it is low in the sky, so light reflected from it passes through more of our atmosphere. Blue and violet light is scattered more easily, so we see a redder Moon. The other is during a total lunar eclipse: longer sunlight wavelengths are refracted by the Earth's atmosphere onto the eclipsed Moon.

Supermoon
A supermoon is a full Moon that coincides with the closest point to Earth in its orbit, causing the lunar disc to appear larger by as much as 14 per cent. The word is rooted in astrology but, given the correct astronomical term is a 'perigee-syzygy Moon', you can see how it caught on. A supermoon also occurs with a new Moon at perigee — but you aren't able to see this one.

The Big Myth — The Moon illusion
Look for the Moon when it is low to the horizon and you may get the impression that it is unnaturally large — this is the phenomenon known as the Moon illusion, and it appears to be more pronounced around full Moon when the maximum area of its disc is illuminated. In reality, the Moon has more or less the same apparent diameter of around 0.5°, whether it is looming over the horizon or riding high in the sky.

One explanation for the illusion arises from our perception of the shape of the celestial sphere above us; instead of a hemisphere, we perceive the sky to be a flattened dome. Consequently the lower the Moon is in the sky, the farther away and larger it is perceived to be. When the Moon is high in the sky we conversely perceive it to be closer to us and therefore smaller in apparent size.

Few people seem to be immune to the Moon illusion, even though the viewer may be fully aware that for any given evening there is actually no appreciable difference in the Moon's apparent diameter, regardless of its height above the horizon.

The Rarest Moon
No doubt you've heard the expression 'once in a blue Moon' — meaning something that is exceptionally rare. But what exactly is a blue Moon, and does our neighbour ever adopt an azure appearance?

When astronomers use the term, they are most likely referring to one of two lunar events — neither of which cause the Moon to turn blue.

Traditionally, a blue Moon is considered to be the third full Moon in a season that has four. Normally, there are only three. The second and more modern interpretation is that it is the second full Moon that occurs in a calendar month, which can happen as a lunar cycle only takes 29.5 days to complete.

Why the discrepancy in definitions? It appears to be the result of a publication mistake that appeared in 1946 that confused the traditional meaning, which dates back to 19th-century editions of the Maine Farmers' Almanac.

And yet there is circumstance that can cause the Moon to truly appear bluish, as it did in the wake of the Krakatoa eruption in 1883, and it is exceptionally rare. The secret is that the atmosphere needs to be flooded with dust particles of a specific size — slightly smaller than the wavelength of red light — and that size alone. These particles scatter red light, causing the Moon to take on a slight cerulean cast.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

To many, the Ringed Planet is the first 'wow' object they glimpsed through a telescope. Paul Money explains how you can see it for the first time.

Saturn by Mark Bell

If there is one planet in our Solar System that captures hearts, inspires minds and invokes joy when seen through a telescope it surely has to be the ringed wonder that is Saturn. Even through a modest instrument such as a 2.5-inch spotting scope it is possible to see that the planet is more than a roundish globe. No other planet comes close to capturing the wonder and imagination of young or old when they see Saturn through a telescope for the first time.

Reactions to the view can be interesting. While running a public astronomy event with Saturn as the 'star', a nine-year-old boy took one look through a 10-inch telescope and, for one cheeky moment, exclaimed it had to be a picture stuck to the end of the tube! A tap on the tube as he took another look put him right: the view shimmered and he stepped back amazed, exclaiming, "Wow it really does have rings!"

It is this joy of discovery when someone takes their first look at the beguiling planet which is so inspiring and moving. Saturn, along with the craters on the Moon, is consistently voted as the favourite things to see through a telescope on outreach evenings.

It is a common mistake to think that you need a large telescope with lots of sophisticated equipment to get the best view of Saturn. The truth is you don't: even a pair of 10x50 binoculars will show that the planet is slightly extended either side of the disc and reveal Saturn's largest moon, Titan, when it is not too close to the planet. Using a 5- to 8-inch reflector or 3- to 5-inch refractor will show more detail. A scope with a long focal ratio of around f/9 to f/12 helps too, as this will make the disc and rings appear larger in the eyepiece.

Stark and Golden
Through such instruments the planet can take on a golden hue, in stark contrast to the gleaming white rings, which are currently angled towards Earth. Within the rings you should look for the Cassini Division, the black gap that separates the outer A ring from the brighter B ring. You might even see the inner C ring at times, if the air currents in our atmosphere are steady to provide good seeing. These certainly aren't the only rings Saturn possesses, but they are the easiest to pick out.

The planet itself may also show a dusky northern belt and a polar haze. Through a telescope you'll also be able to bag a few more of Saturn's moons, most likely Rhea, Tethys, Dione and Iapetus. Larger telescopes reveal more subtle detail on the planet, finer detail in the rings and three more moons: Mimas, Enceladus and Hyperion.

If you are showing the view to youngsters, make sure they can reach the eyepiece; perhaps keep a stool or sturdy chair handy for them. Not everyone finds it easy to keep one eye closed as they look through the eyepiece either, so an eye patch can be a useful aid. Some children (and even adults) can struggle looking through an eyepiece. If that's the case, try getting them to look through an empty toilet roll tube; it's surprising how effective this can be in getting them ready for the view through a telescope.

With Saturn best placed during the summer months, now is the time to plan a barbecue, get your friends and neighbors round, let the kids stay up a little later than usual and take a look at the second largest planet in our Solar System. With the added bonus of the spectacular ring system, it is sure to impress.

Getting the Best View — How to Make the Most of Observing the Ringed Planet
A good clear southern horizon is a must for spotting Saturn. Use binoculars first to home in on the planet, then a modest telescope such as a 5-inch reflector or a 3-inch refractor to gain a closer look. When using a telescope, make sure everyone can reach the eyepiece. With reflectors in particular, you can usually rotate the tube to bring the eyepiece to a better position, or have a stool or chair handy. Don't use too high a magnification: it's better to ensure the view remains sharp, even if that means keeping the magnification lower than you'd like.

Top 10 Saturn Facts
As well as being a beauty, the ringed wonder is also a fascinating world.

1. Saturn has 62 confirmed moons.
2. The planet is tilted on its axis by 26.7° and therefore has seasons. Each lasts just over seven years because Saturn takes 29.45 years to orbit the Sun.
3. Saturn is a gas giant planet; it is mainly made up of hydrogen and helium. It's thought that a rocky core exists at its centre.
4. On average, Saturn is 9.5 times farther from the Sun than Earth is.
5. Each day on Saturn is only 10.55 hours long. This means that there are 24,470 Saturnian days in one Saturnian year — that's a lot of sunrises and sunsets!
6. Saturn is slightly flattened: its equatorial diameter is 120,536km while its polar diameter is 108,728km. You could fit 9.5 Earths across its disc.
7. The ring system out to the A ring is 273,550km wide, but only 1km thick.
8. Saturn is a windy planet, with gusts measured by Voyager at 1,800km/h.
9. Titan, Saturn's largest moon, has a nitrogen atmosphere and liquid lakes of methane on its surface.
10. Roughly every 30 years, a great white storm appears in Saturn's northern hemisphere.

About the Writer
Paul Money is the BBC Sky at Night magazine reviews editor and an expert on running astronomy outreach events.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

A familiar sight in our skies from ancient times, the Moon is threaded through humanity's history.

Bulliadus Crater by Mark Bell

The source of our ocean tides, subtle chronobiological cycles and the only other world that humankind has so far set foot upon, the Moon seems a familiar and tangible place. A quarter of Earth's diameter and just a quarter of a million miles away, it's 100 times closer than Venus. Given its proximity, brightness and large apparent size, it's easy to see why the Moon has enchanted humankind for centuries.

Before the emergence of widespread street lighting, the Moon was the primary source of light for nocturnal activities. Its sheer size and regular cycle of phases made it an obvious timepiece to our ancient ancestors, forming the basis of some early calendars, and in various cultures the Moon either had deities associated with it or was considered to actually be one. In the following centuries, when astrology and astronomy were one and the same, it continued to bear a supernatural significance, marking when certain activities and plans would go well — and when they were doomed to fail.

Pre-telescopic observers noticed an unchanging pattern of darker patches that would later become known as maria, or 'seas', because they were assumed to be vast bodies of water. They act as a Rorschach test for different cultures — the face of the 'Man in the Moon' observed in Western tradition, the 'Rabbit' pounding rice of East Asian folklore, or the 'Lady Reading a Book' from the southern hemisphere, to give just three examples.

Until the middle ages, the Moon was believed to be a smooth sphere, neatly slotting into the Aristotelian view of the 'perfect heavens'. It wasn't until after 1609, when Galileo turned his telescope to the Moon, that this perception was undone.

Galileo was not the first to examine the Moon through a telescope — that accolade falls to Englishman Thomas Harriot, whose sketches predate Galileo's by several months — but he was the first to publish. In his Sidereus Nuncius, Galileo revealed a world pockmarked with craters and mountains. He had seen that the terminator, the line that divides lunar day and night, was often jagged, correctly inferring that this irregularity must result from shadows cast by topographical features.

About a dozen lunar landforms can be distinguished with a keen eye. A typical pair of binoculars, if suitably steadied, will transform your view of the Moon into a scarred, airless world, and most likely will give you a better view than Galileo had in the 1600s. Through even the smallest modern scope innumerable impact craters appear, often fringed by long rays of ejecta. Alongside them sit grand basins of solidified lava, soaring mountain peaks, curious fissures and escarpments — it's a whole new world to explore.

Locked on Earth
You don't need a telescope to reveal that night after night we always see the same lunar features staring back at us. This is because the Moon has a synchronous rotation with respect to Earth, meaning that spins once on its axis in the same 27.3 days (the sidereal month) it takes to complete an orbit of our planet.

This is no coincidence. Earth's gravitational pull on the Moon has caused a bulge in the body of the Moon itself, similar to the tides in Earth's oceans. This bulge unbalanced the Moon's gravitational force, slowing its rotation until the bulge aligned with the Earth. Despite its appearance in the sky, our Moon is nowhere near round; it is closer to a lemon shape.

A consequence of this 'tidal locking' is that for much of human history the Moon held a closely guarded secret: no one knew what the far side was like. This didn't change until 1959, when the Soviet Luna 3 probe became the first to pass an image of the hitherto unseen side.

In a memorable episode of The Sky at Night broadcast on 26 October 1959, Patrick Moore announced the success of the Soviet mission, revealing the first shadowy photographs of the Moon's far side live on air. Luna 3's imagery was crude by today's standards, but it revealed that the 'dark side' was strikingly different in a number of ways.

While 35 per cent of the Moon's Earth-facing hemisphere is covered with mare lava, very little molten material made it to the surface on the far side, so maria account for just one per cent. It's thought this is because the far side's crust is thicker — it may be up to twice as thick as that of the near side — possibly due to the slow accretion of a companion satellite after an impact. This theory seems to be supported by the discovery of the far side's 3.9 billion-year-old South Pole — Aitken Basin, over 2,400km wide and around 13km deep. To date, our best views of the Moon come from NASA's Lunar Reconnaissance Orbiter, now in its sixth year of operations and, at the time of its launch, the first US mission to the Moon in 10 years.

The Sun Always Shines
It's equally obvious that the illumination of the Moon's Earth-facing hemisphere changes over the course of the month — a word, incidentally, that we get from 'Moon'. Although the Sun is always shining on a full half of the Moon, the proportion of the lit side we are able to see depends on where the Moon is in its orbit around Earth, giving rise to the phases we see.

Imagine you are looking down on the Earth, Moon and Sun from above. When the three line up with the Moon in the middle, the Moon's lit half points away from us on Earth, producing a new Moon. Slowly emerging from its new phase into the evening sky, the lunar crescent thickens from one day to the next. The term 'waxing' is used to indicate this thickening phase. The waxing crescent leads to the Moon appearing as an illuminated semicircle roughly a week after new.

This is somewhat confusingly called 'first quarter', referring to the Moon's position in its 29.5-day orbit rather than proportion of its disc is illuminated from our vantage point on Earth. The bulging phases after first quarter are known as waxing gibbous. These increase in size until roughly two weeks after new, the Moon is on the opposite side of its orbit from the Sun and appears fully lit as a full Moon. The point of new and full Moon, when our planet, satellite and star are aligned, is technically known as a 'syzygy'.

After full Moon the phases reverse, and the illuminated part of the Moon begins to shrink or wane. After passing through the waning gibbous phases, the Moon reaches the three-quarter point of its orbit, giving rise to the 'last quarter' phase. The Moon takes the appearance of a semicircle once again, although it's the opposite half that is illuminated than that at first quarter. After this, it takes approximately a week for the Moon to go through its waning crescent phases, visible in the early morning sky, before it once again becomes new again. It takes 29.5 days for the Moon to return to complete this cycle of phases or 'lunation', slightly longer than it does to complete an Earth orbit. This is known as a synodic month.

Ellipse and Eclipse
The Moon's elliptical orbit is inclined to Earth's by an average of 5°. This means that on most of the occasions that a full Moon occurs, it actually passes above or below the shadow Earth casts into space. But in the instances that the full Moon passes into Earth's shadow we see a different phenomena: a lunar eclipse.

Because the Sun is much bigger than Earth, it splits our planet's shadow into two parts: the darkest, called the umbra, and a lighter outer ring, called the penumbra. The intensity of a lunar eclipse depends on how much of the Moon passes into Earth's shadow, and which part of the shadow it passes through.

In a total lunar eclipse, the entire Moon passes through the penumbra and into the umbra, gradually darkening until it is completely covered, a point known as totality. During totality no sunlight shines directly on the Moon, but some is refracted onto it via Earth's atmosphere. As our atmosphere filters out blue light, the Moon often gains a strange orange-brown colour.

As the Moon goes into eclipse and dims, the sky gets darker too. You may not have realised how bright a full Moon can be. It lights up the sky around it with a blue haze, out of which only the brighter stars are visible. During a total lunar eclipse, the darker Moon means that the fainter stars can come out and we end up with the eerie sight of a deep-red Moon surrounded by twinkling stars.

There are two other types of lunar eclipse: partial, where only a portion of the Moon passes through Earth's dark umbral shadow, and penumbral, where part of the Moon only passes through the lighter, outer shadow. Partial eclipses can be quite noticeable, but penumbral eclipses often only cause a slight dimming.

When the same thing happens at new Moon the opposite occurs, and we may see a partial or total solar eclipse. By staggering coincidence, right now the Moon is both 400 times smaller than the Sun and 400 times closer, meaning that they appear to be the same size in the sky. The fact the Moon only just covers the Sun during a total solar eclipse allows us to glimpse our star's ghostly outer atmosphere, the corona.

A Changing Relationship
Life on Earth owes a lot to our rocky companion. Without it, our planet's axis would tilt wildly between 0° and 85°, albeit over a period of a million years, sending our hemispheres veering between chaotic ice ages and searing hellscapes. It would have been a death sentence for evolving life.

But our relationship with the Moon is becoming increasingly distant. When it formed, the Moon was only 22,500km from our planet. Today, it's nearly 10 times farther away and getting more distant by 3.8cm a year — around the same rate as your fingernails grow. As a result, Earth's spin speed is slowing down and our days are getting longer.

Eventually, there will come a point when the length of the day and the month will be the same, and the Moon will cease to cross our skies. There will be no new or full Moon, only a small static disc in the night sky visible from one side of the planet, a situation we see today in the Pluto-Charon system. By the time that happens, humans will hopefully be looking out at other moons from distant planets.

The Major Classes of Lunar Features

Valleys
There are 14 official valleys on the Moon, the longest around 600km. Most are named after nearby craters. One of the most familiar is the 180km-long Vallis Alpes (pictured), which cuts across the northern Montes Alpes and almost connects the Mare Imbrium and the Mare Frigoris.

Seas
These vast dark plains of solidified magma are notable for both their dark appearance and the fact that they are largely absent from the Moon's far side. One of the most distinct is the 560km-wide Mare Crisium (pictured) which is just visible to the naked eye.

Craters
The ubiquitous lunar feature, varying in size from microscopic pits to sprawling depressions up to 350km in diameter — anything larger is a basin. Some were formed through volcanism but the majority, like Tycho (pictured) are the result of ancient impacts.

Basins
The oldest and largest impact craters on the Moon, exceeding 350km in diameter. All lunar maria are found within them. The South Pole-Aitken Basin on the Moon's far side holds the record for being the largest, at around 2,400km; the biggest on the near side is the Imbrium Basin, shown here, which stretches across 1,160km of the lunar surface.

Mountains
The Moon's peaks are named in two ways: 'Montes' for mountain ranges and 'Mons' for singular peaks and massifs. The most spectacular of the 18 named lunar ranges is the gently curved, 600km-long Montes Apenninus (pictured), which form the southeastern edge of the Imbrium Basin. Mons Huygens, the Moon's tallest mountain at 5.4km, soars skyward here.

The Big Myth — The Dark Side of the Moon
The phrase 'dark side of the Moon' may evoke fond memories of Pink Floyd's 40-year-old prog-rock album to the baby boomer generation, but in an astronomical context it's often used to refer (erroneously) to the Moon's far side. The phrase is something of a misnomer, since the lunar far side goes through the same cycle of illumination as the phases of the Moon seen on the Earth-facing hemisphere. Technically, the far side is the 'dark side' at the instant of full Moon. The only places on the Moon's surface permanently bathed in shadow are a few deep craters at the north and south poles.

Where Did the Moon Come From?
Most scientists now believe that the Moon was formed around 4.5 billion years ago when an object the size of Mars (and since named Theia) collided with the early Earth, giving it a glancing blow. The impact spewed debris into Earth's orbit, which coalesced to form the Moon at just the right distance to be an independent body; any closer and Earth's gravity would have pulled the material back.

This theory was born from the chemical analysis of lunar samples returned by the Apollo missions, which showed a remarkable similarity between Earth's composition — hinting at a common heritage. But there is a problem: the compositions look too similar. If this collision occurred, the Moon should have more of Theia's material and should therefore be more different from Earth.

The Apollo samples were obtained from a very small area - could this explain the similarities? It would seem not, because we do have other lunar material. The Russian Luna programme returned 0.33kg of Moon samples and we also have a number of lunar meteorites. Analysis of this material brings up a similar problem, it is just too similar to the composition of Earth.

So where does this leave the collision theory? It still has a lot of support, but what would be a great help is having more lunar samples from known but more varied locations.

What's Our Moon Made Of?
Our natural satellite has a small core composed predominantly of iron, a distinct mantle, and a crust of varying thickness comprised of anorthosites and basalt.

Moon Facts

• Age: 4.5 billion years
• Diameter: 3,475km
• Mass: 0.0123 Earths
• Average distance: 384,400km
• Average orbital velocity: 3,679km/h
• Orbital period: 27.3 Earth days
• Lunar cycle: 29.5 Earth days
• Surface gravity: One-sixth that of Earth

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Will Gater takes us on an observing tour across the sparkling summer night skies.

Milky Way over Pinnacles by Steve Peters

Summer's balmy nights are short but they pack in some glorious celestial sights. There are many deep-sky objects nestled in the rich star fields of the Milky Way and these will be our destinations on this seasonal star hop. The best time to take this tour is in the last week of June, when the Moon is out of the way. You can choose whether to spread the 15 objects here over a few nights, or observe them all in one. If you feel like doing them in a single session, to make maximum use of the darkness during June's short nights we've chosen a route that takes you through the 15 in the order that they reach their highest point in the sky.

1. M3
Let's kick off our observing session over in the western sky just after midnight. Hopefully the Moon isn't around and there are hours of clear skies ahead. Mag. +0.2 Arcturus (Alpha Boötis) is blazing away and it's the signpost we need to find our first object, globular cluster M3 in Canes Venatici. Once you've found Arcturus, imagine a line between it and mag. +2.9 Cor Caroli (Alpha Canum Venaticorum). The cluster is just less than halfway along this line.

2. M13
We've got a bit of a trek to our next object, the spectacular globular cluster M13 in Hercules. Thankfully we can get there with a few simple star hops. Probably the easiest method, from M3, is to use mag. +3.6 Rho and mag. +3.5 Delta Boötis as pointers. Scan along a line from Rho Boötis through Delta Boötis for just over 27° and you'll come across M13. The cluster is easily visible in binoculars from dark skies and through a small scope it appears as a fuzzy ball of faint light; larger aperture scopes will fare better at resolving the cluster's myriad stars.

3. M92
Once you've enjoyed M13 it's time to move to another globular cluster, M92, which is about 9.5° away. It's not as impressive as M13 in binoculars, but it's fairly easy to locate nevertheless. Just sweep along a line between M13 and mag. +3.8 Iota Herculis. You can also find the cluster with a telescope through a series of simple star hops: head northeast from mag. +3.1 Pi Herculis to mag. +4.6 69 Herculis and then onto mag. +6.0 HIP 84656, mag. +7.4 HIP 84559 and finally mag. +6.8 HIP 84118, which is just over 1.5° from the cluster.

4. Epsilon Lyrae
Having admired three fine globular clusters we're going to switch to a completely different type of object, the wonderful multiple star system of Epsilon Lyrae. From M92, head eastwards towards brilliant mag. 0.0 Vega (Alpha Lyrae). From Vega it is only a short hop to Epsilon Lyrae, which makes a triangle along with Vega and mag. +4.3 Zeta Lyrae. Epsilon Lyrae is most definitely a telescopic object. With a medium to high power eyepiece and a good-sized scope you should have little trouble seeing the two pairs of stars in the system.

5. The Ring Nebula
While in Lyra, there's one object that we really must visit and that's the charming Ring Nebula, M57. This is what's known as a planetary nebula, formed when a star like our Sun ejected its outer layers towards the end of its life. It appears as a little grey ring through the eyepiece. To find it we don't have to go far, though you will need a telescope and a medium-power eyepiece to see it well, as its angular diameter is rather small. You'll find M57 about 70 arcminutes along a line between mag. +3.3 Sulafat (Gamma Lyrae) and mag. +3.5 Sheliak (Beta Lyrae).

6. M22
It's time to head south from Lyra and into Sagittarius, and the beautiful Milky Way star fields in and around it. At the end of the month, the Milky Way will be low in the south at about 01:00 BST (00:00 UT). Our first object here is magnificent globular M22. To find it, first locate the famous Teapot asterism. The handle of the teapot is the key to finding M22. Imagine a line from mag. +3.3 Tau Sagittarii towards mag. +2.1 Nunki (Sigma Sagittarii). If you extend this line for about 5° beyond Nunki you'll reach the cluster.

7. The Lagoon Nebula
Next on our tour of this part of the sky is the wonderful Lagoon Nebula, M8. There are several ways you can go about tracking it down. Under dark skies it's visible to the naked eye, so if you're using binoculars you should be able to pick it out fairly easily about 6° above the 'spout' of the Teapot asterism. If you're using a telescope you'll find the glowing nebula and its sparkling star cluster by slewing roughly 7° to the west of M22. If you get stuck, remember that the nebula forms a rough isosceles triangle with mag. +2.8 Kaus Borealis (Lambda Sagittarii) and mag. +3.8 Mu Sagittarii.

8. M23
Heading away from the Teapot asterism, we're now traversing some of the dark dust lanes that criss-cross this region of the Milky Way. We're going in the direction of an exquisite open cluster, made of some 150 stars, catalogued as M23. If you're using binoculars, scan a line from Mu Sagittarii to mag. +3.5 Xi Serpentis. You'll find M23 just less than halfway along. With a small telescope you can star hop from the Lagoon Nebula to the glittering M23 by using four stars as waypoints: mag. +5.8 HIP 88298, mag. +6.3 HIP 88760, mag. +6.8 HIP 88362 and mag. +7.5 HIP 88297.

9. M25
From M23 we're going to cut right back across the band of the Milky Way to another lovely open cluster, M25, which is also in the constellation of Sagittarius. As you scan east across the sky with binoculars, take a moment to admire the stunning, densely packed star fields located roughly halfway between M23 and M25. Finding M25 with a small telescope is also fairly easy: simply point your finderscope at the 5th-magnitude star HIP 90806 and you'll find the glittering stars of M25 sitting around 45 arcminutes to the south of it.

10. The Eagle Nebula
Our final object on this leg of the tour is located a little higher up in the sky. It's the Eagle Nebula, M16. To get there we need to jump across the border from Sagittarius into the neighboring constellation of Serpens. Start by tracking roughly north from M25 to mag. +4.7 Gamma (g) Scuti. Once there, move west and up a little using mag. +6.7 HIP 90281 to guide you toward the nebula. With a small telescope you should have no problem seeing the cluster of stars in M16 and maybe a hint of the nebulosity itself.

11. The Wild Duck Cluster
We're now entering the third and final leg of our tour, which we begin in the constellation of Scutum, the Shield. This beautiful region of the summer night sky is home to edge of the Scutum Star Cloud and can be seen easily in binoculars. For a truly breathtaking view, use a telescope with a low-power eyepiece so you can really appreciate the open cluster and its starry environs.

12. The Coathanger
To get to our next object we're going to meander our way up the band of the Milky Way. The Coathanger, also known as Brocchi's Cluster, is a lovely grouping of stars that, you guessed it, looks like a coathanger — albeit an upside down one. To reach it from M11, use binoculars to work your way along the rich star fields in Aquila until you get to mag. +0.8 Altair (Alpha (a) Aquilae). Using Altair and the nearby mag. +2.7 Tarazed (Gamma (g) Aquilae) as pointers, head slightly northwest for about 12.5°. Dark skies and a good pair of binoculars are all you need to enjoy this gem.

13. The Dumbbell Nebula
Next up is the fascinating Dumbbell Nebula, M27, which sits in the constellation of Vulpecula. We don't have far to go, but we will need a change of equipment, as a small scope is the best instrument for observing this planetary nebula. There are ways you can star hop to M27, but an easy one is to simply point your scope's finder at the 3rd-magnitude Gamma Sagittae and track north for just over 3°. In a small scope M27 looks like a smudge of light, but in 6-to 8-inch instruments its dumbbell shape becomes much more obvious.

14. Albireo
If you've reached this point having observed all the objects so far in one night, we salute you! Your reward will come in the form of one of the most beautiful double stars in the whole night sky, Albireo (Beta Cygni). Albireo is 3rd-magnitude, meaning it is easily visible to the naked eye. It sits at the head of Cygnus, the Swan, which is marked out by a large 'cross' of bright stars with mag. +1.3 Deneb at one end and Albireo at the other. Through a telescope, at high magnification, the two stars sparkle gold and blue — a wonderful sight on a warm summer evening.

15. M39
We're now at the end of our journey and chances are, if you've been observing all night, the sky is now starting to lighten. We'll end our tour across the summer sky by looking at a lovely, if often overlooked, open cluster: M39. To find it with binoculars follow the body of Cygnus all the way from Albireo to bright Deneb, passing mag. +2.2 Sadr (Gamma Cygni) as you go. From Deneb, imagine a line running all the way to mag. +3.8 Alpha Lacertae in the head of Lacerta, the Lizard. M39 is situated almost exactly at the midpoint of this line.

Summer Astrophotography: Objects to Photograph in This Season's Night Skies
The nights may be short at this time of year but that doesn't mean there aren't plenty of imaging opportunities. Noctilucent clouds are extremely photogenic; a DSLR or compact camera on a photographic tripod should capture them well. Using a wide-angle lens and an exposure of between two and 10 seconds should be perfectly sufficient to reveal most displays.

The summer Milky Way in the constellations of Sagittarius, Scutum, Scorpius and Ophiuchus is also a fine photographic target in June. If you're just starting out in deep-sky astrophotography this region offers many bright and beautiful objects to cut your teeth on; the Lagoon Nebula, M8, is a good example, though you will need a clear southern horizon and excellent transparency for the best images of it.

For more experienced imagers, fainter objects such as the Cocoon Nebula (IC 5146) in Cygnus and the Iris Nebula (NGC 7023) in Cepheus provide a satisfying challenge. If you use narrowband filters in your deepsky imaging setup, old favorites such as the Eastern Veil Nebula (NGC 6992), the Witch's Broom Nebula (NGC 6960) and the Crescent Nebula (NGC 6888) — which are all in Cygnus — are also well placed this month.

Noctilucent clouds
Keep a close eye out for these high-altitude electric blue displays.

The twilight skies of the summer months are occasionally adorned with beautiful, glowing wisps of light known as noctilucent clouds. These polar mesospheric clouds, to give them their scientific name, reside high up in our atmosphere at an altitude of around 80-85km. They are clouds of minute ice crystals and it is their great height that causes them to shine — 'noctilucent' simply means 'night shining'.

While ordinary clouds, much lower down in our atmosphere, appear silhouetted against the glow of twilight, the high altitude of noctilucent clouds means they are still illuminated by the Sun, and so scatter the sunlight down towards us on the ground. It's thought that the tiny ice crystals may form on microscopic pieces of meteoritic dust, deposited into our atmosphere by the countless meteors that zip through this region.

Noctilucent cloud displays are usually seen in the UK during late May, June, July and early August. Unfortunately, predicting when a good display will be visible is not easy, so your best bet is to be vigilant and look out for them during the hours after sunset or before sunrise throughout the summer. From the UK, it's the northern horizon that you need to monitor closely for any possible noctilucent cloud activity. Some displays can be very weak and may only show up on camera, while others are bright and easily visible to the naked eye as bluish-white ribbons of light, perhaps containing striking ripple or tendril-like structures.

They are a wonderfully dynamic phenomenon and appear to change minute by minute — some displays look like flowing waves of light crashing over the horizon. Binoculars, or a fixed camera taking still images every five to 10 seconds, will help you pick out any changes in shape and structure, but be very careful not to accidentally observe the rising Sun.

About The Writer
Will Gater is an astronomy writer and journalist. He also appears on TV and radio to talk about space. Find him on Twitter: @willgater

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Zhang Xian shooting at a tiangou, a legendary Chinese
creature thought to eat the sun during an
eclipse [Public domain], via Wikimedia Commons

Total solar eclipses belong to a rich and diverse cultural heritage steeped in myth and superstition. Even today, the sight can stimulate primitive receptors in our bodies to react when we see daylight suddenly turn dark and behold the preternatural glow of the solar corona surrounding the "black hole" of the New Moon.

Little wonder many cultures across the globe imagined the event as a beast (dragon, frog, wolf, snake, giant, ghoul ... you name it) devouring the Sun, and made noises (like banging drums) to scare the offender away. In time the beast gave way to superstitious beliefs, and we can still see age-old rituals re-enacted. For example, during the October 1995 totality over northern India, 1 million people bathed in the sacred waters in Kurukshetra, believing that doing so would bestow blessings of peace unto them and other wandering and unhappy souls. That may sound funny, but it's no different from the age-old tradition (superstition) of voting along party lines; we just put our faith in a different kind of promise in the belief that life will suddenly get better.

During the 2016 totality over Indonesia, I met locals who were told (as children) that if they looked at the Sun directly, ghosts might steal them away when the sky turned dark; so it was best for them to stay indoors with the curtains closed. When older they learned to watch the partial phases of totality indirectly — reflected in a dark bowl of water. This behavior, I thought, is culturally no different from parents employing the idea of Santa Claus to instill fear in children who might otherwise behave badly — until they know better.

The world over, superstitions abound when it comes to pregnant women and total solar eclipses. The women are cautioned to stay indoors with the curtain closed or their unborn child might be born deformed, or blind, or ... well, does it really matter what they're told? The root superstition stems from the fear that the mother-to-be may do herself harm if she looks at the Sun (which is true, if she does so without proper eye protection), and therefore will not be able to care for her unborn child.

On the opposite end of the scale is the belief in totality's healing power. For instance, during the July 2009 total solar eclipse over Pakistan, some parents with disabled children buried them up to the neck in sand, hoping the event would help to heal them. It's no different, really, than bathing in sacred waters; it's another cultural belief that helps one's soul in a time of despair. Drastic? Yes. But who's to judge?

Some Native Americans will not look skyward during an eclipse largely out of respect. When a total solar eclipse occurs, it steals daylight from the sky causing an imbalance in what's known as the "cosmic order." Looking sunward at this time is regarded as taboo. The Sun is sacred and should not be watched for long; by staying inside and not looking skyward during an eclipse, one respects the Sun, allowing it to undergo a rebirth ... in private. Perhaps just as one shouldn't watch a couple consummate a marriage, one shouldn't interfere with the Sun as it undergoes its sacred and intimate union with the Moon.

On the other side of the coin, there's a fear component to this tradition. Watching a solar eclipse can adversely affect the mind, tilt life out of balance, and invite evil into one's life. In essence, one is left to weigh a minute or two of totality against a potential lifetime of turmoil and chaos. It's like the dieter's creed: a moment on the lips, a lifetime on the hips ... You decide!

Fears and superstitions will undoubtedly still lurk in the Moon's shadow when totality occurs over parts of the United States on August 21, 2017 — especially with the uninformed. Most of us, however, will have, by then, read articles and blogs, had casual conversations with experienced or prospective eclipse watchers, and learned proper safety measures (for eye protection) which, if followed, will provide a completely harmless, enjoyable eclipse experience.

As for the various traditions that continue to linger, what are they but "good lies" spoken by the uninformed with an aim to either protect those they love from forces unknown or to help them in times of need. "Unknown" is the key word. With education, we can help people disperse the mists of mystery and learn how to appreciate one of the world's most visually rewarding natural spectacles — totality.

CAUTION: Never look at the Sun, either directly or through a telescope or binocular, without a professionally made protective solar filter installed that completely covers the front of the instrument, or permanent eye damage could result. When using a truss tube telescope to view the Sun, both a properly fitting solar filter and light shroud are required.

Stephen James O'Meara is an award-winning visual observer, whose writings, lectures, and numerous books on amateur astronomy have inspired observers across the globe to see the sky in new and wonderful ways. A contributing editor for Astronomy magazine, Stephen is an avid "eclipse chaser", having witnessed a dozen total solar eclipses dating back to 1959 (when he was 3 years old).

Over the past thirty years, I've made several successful eclipse chases — last-minute dashes to escape clouds threatening to obliterate the spectacle of the Moon obliterating the Sun — but none were as hectic and heart thumping as the one during the March 9, 2016, total solar eclipse.

My partner Deborah Carter and I began planning for that event a year in advance. The March 9th path of totality swept across parts of Indonesia and the Pacific Ocean. Weather studies led us to select Ternate, a small volcanic cone jutting from the sea in northern Indonesia, as the prime viewing location. We arrived four days before totality, and, despite an atmospheric "monkey wrench" (El Niño), we enjoyed cloudless bliss until the day before totality.

That morning we awoke at dawn to partly cloudy skies. The once brisk trade winds had stopped, and the air felt muggy and hot. By late afternoon, storm clouds had gathered, only to unleash torrents of rain that lasted until midnight. Figuring the worst was over, we went to bed feeling cautiously optimistic — only 8 1/2 hours to go before the partial phases of the eclipse were to begin, and the rains had stopped.

When eclipse morning dawned clear, we cheered and rushed to the hotel's roof to set up our cameras, filters, and tripods. Two new friends from Java (Adrian and Heni Smith) joined us to watch first contact under a cloudless sky. About 20 minutes into the event, however, I saw a dark gray mass building on the eastern horizon. The mass turned into broken cloud, which began creeping toward the Sun at an uncomfortable rate. About 10 minutes later I saw the first cloud fragment brush past the Sun.

Deborah noticed my concern and asked what I thought.

I asked our new friends if they had a car.

They did.

I suggested we leave.

Deborah asked when.

"Now!" I replied.

We had everything packed in a flash and took an elevator to the ground level. Adrian got the car, we stuffed it with gear, crammed ourselves in, and made a mad dash toward blue sky.

But first we had to negotiate a maze of one-way streets jammed with motorbikes, cars, and crisscrossing pedestrians. Precious minutes passed before we got onto the main road. A nail-biting five-mile sprint took us to the southern edge of the island, where clouds still covered the Sun — just barely — we were literally right on the edge.

Fifteen minutes to totality.

But we had nowhere else to go ... except to the water. We saw a beach beyond the cliff, and Deborah had sighted an access road to it nearby. We made a five-point turn, zipped down the road, slipped into the alley, and bounced into a little seaside village.

Still not good enough; clouds continued to hide the Sun.

Ten minutes to totality.

Aha! There were boats and people up ahead. Heni swiftly negotiated with happy locals as we waded out to a narrow wooden fishing boat with pontoons.

Six minutes to totality.

After removing a canopy, we got on the boat, and the owners started to paddle.

My heart sank.

Deborah asked if the boat had a motor.

It did, but the tide was out, so they had to push beyond the reef.

Three minutes to totality.

Seconds felt like hours. I pleaded that they start the motor. They agreed.

After a few tugs on the cord, the one-cylinder engine coughed to life, and we chugged southward at a possum's pace.

Kluck ... kluck... kluck....

We were traveling at about the same speed as the advancing cloud edge, which just covered the Sun. Another vital minute passed without gain.

Then I noticed a hole forming in the clouds. Gesturing, I stood up and shouted, "Head west!" After hurtful moments of confusion, the crew finally understood and set off on the new course.

Seconds before totality, we saw the Sun break free of cloud. We began whooping as the diamond ring formed, the Sun winked out, and the gossamer petals of the Sun's corona blossomed into view. After that, emotion overwhelmed thought. I'm not sure if sanity ever returned.

Thanks to our combined efforts, we watched totality for nearly three minutes through a magnificent hole in the clouds.

The lesson: if you truly want to maximize your chances of seeing this rare event, don't rely on the luck of the devil; if clouds threaten, chase blue skies as if the devil were chasing you!

Stephen James O'Meara is an award-winning visual observer, whose writings, lectures, and numerous books on amateur astronomy have inspired observers across the globe to see the sky in new and wonderful ways. A contributing editor for Astronomy magazine, Stephen is an avid "eclipse chaser", having witnessed a dozen total solar eclipses dating back to 1959 (when he was 3 years old).

One of the nicest aspects of winter observing is the early sunsets and long nights. You can be outside and enjoy an hour or so of astronomy, and still be in early enough that mid-week viewing is an easy habit to acquire. All we need are clear skies. When you have them, get out and enjoy!

I find nothing more pleasing than an easy star hop from one great target to another. Take your binoculars or telescope out this week for a short but fun hop to four big and bright open clusters full of variety, as well as some interesting challenges. These are clusters that will become staples of your winter observing routine.

Gemini and Auriga

Find Gemini and Auriga rising above the eastern horizon in the early evening. M35 (discovered by Philippe Loys de Chéseaux) is the lone Messier object in Gemini. The trio of M36, M37 and M38 form a nearly straight line, equally spaced in Auriga. Charles Messier discovered them while searching for comets from his observatory in Paris, France. He discovered 16 comets, but is more famous for objects he cataloged as "not" comets, so he wouldn't mistake them in his search. The list of non-comets became famous at the Messier Catalogue, 110 objects that represent the brightest and arguably most interesting deep sky targets in the northern skies.

M35 with NGC 2158 at lower left. Image courtesy André Hartmann.

Let's begin with M35 in Gemini. It is very easy to locate off of one of the Twin's feet. Train your binocular or telescope finder on Eta Geminorum - the last star in the chain that begins with Castor. You should see the big open cluster as a bright fuzzy patch of light to the star's north-northwest. At magnitude 5.1, it is quite bright, so much so that there are reports of observing it without optical aid, meaning, naked-eye. Try this from a dark sky. In small binoculars, such as a 7x35, it appears as a 25' fuzzy patch with hints of resolution in periods of excellent seeing. In an 8" telescope it is best viewed at low power, so the cluster does not entirely fill the field of view. One description has it as somewhat donut shaped, with fewer stars in the center. The cluster is about the size of the Full Moon, has at least 120 stars of magnitude 13 or brighter, and is at a distance of 2800 light years. Do you see a dim unresolved glow 15 arcminutes to the big cluster's southwest? That's another open cluster, NGC 2158, 10 times older and five times more distant! NGC 2158 is a nice treat coupled with M35!

Use the finder chart at the start of this article to hop up from M35 toward Auriga, between its two closest stars, but stay on the M35 side. Your finder or binocular should show what most observers consider to be the prettiest open cluster, M37.

M37. Image courtesy Ole Nielsen.

M37 was discovered before 1654 by Italian astronomer Giovanni Battista Hodierna. The brightest of the three Messiers in Auriga, it is a very evenly distributed open cluster, with hundreds of stars of similar magnitude. The cluster has over 150 stars brighter than magnitude 12.5. It lies 4500 light years from us, and, with an overall magnitude of 6.2, it has been seen naked-eye. One observer has seen it in 8x21 binoculars from skies limited to magnitude 3. That's quite an accomplishment, but you should use larger binoculars or a telescope to enjoy the cluster at its best. Here is a nice description by Michael Geldorp using an 8" f/6:

"Magnificent cluster. Large and very rich cluster. The stars in M37 seem to form streams flowing outward from the center and there appears to be a relatively starless area near the center. Unbelievable sight at 98X with the cluster more than filling the field of view. There is a yellowish/orange bright star near the middle of M37."

Move just across the constellation line now, to M36, and you'll see a dramatic difference in appearance compared to M37.

M36 courtesy NOAO.

M36 will appear smaller, and sparse by comparison. It too was discovered by Hodiema. It shines at magnitude 6.3 and is 4,100 light years from us. Its size, though, is half that of M37. The difference will be very apparent. It has been reported as a threshold object naked-eye. Try for it that way from your darkest skies. In 7x35 binoculars, observer Lew Gramer reports: "This open cluster under these skies showed as a mere 15' irregular fuzzy patch NE of a pretty grouping of seven mag 5-8 stars, all lined up along a 2-degree path roughly North/South." Michael Geldorp in his 8" f/6 reports: "Nice bright cluster with streams of stars that give it the appearance of a crab to me. Less impressive than M 37, this cluster has fewer stars but more relatively bright ones. Located in a rich part of the sky."

The last of our clusters is M38, which is reminiscent of M35 in that it has a smaller open cluster paired in the field of view.

M38 (above) and NGC 1907. Courtesy Sloan Digital Sky Survey

M38 is listed at magnitude 7.4, so the few "visual" observations (naked-eye) I've found are beyond the reach of most normal humans, but there are reports. In fact, one report says all four of these Messiers are visible at the same time, in one view, from a very dark (magnitude 6.7) location. I'll have to try it. What I do find reliable and interesting is the excellent observation by Michael Geldorp (again): "Large and rich cluster best seen at 49X. Not as many bright stars as M36 but richer in fainter stars. There is a conspicuous Y shaped asterism in the central part of M38. 98X showed more stars but the grandness of the cluster is lost with high powers. Striking contrast with nearby NGC 1907, reminiscent of the M35-NGC 2158 pair. 60-70 stars seen at 98X."

The cluster was also first observed prior to 1654 by the Italian Hodierna. Its 4,200 light years away and is nearly as large as M37 at 24 arcminutes. Unlike NGC 2158 near M35 thought, NGC 1907 is the same distance from us as M38.

All four Messier open clusters are around 4,200 light years distant. To give you an idea of what these clusters' distances mean, if we were to view the sun from within M38, it would appear as a magnitude 15.3 star. Go search for one in your telescope. Here's another fun fact, and chuckle — none of these four Messiers was actually discovered by Charles Messier!

I hope you've enjoyed this "hop". There are lots more, clusters, bits and pieces of nebulae strewn through our nearby home locale, and strings and chains of galaxies to explore.

Till next time under the stars,

Mark Wagner

Halloween is a great time to share astronomy. It's an appropriate time to do it as well. With families coming out in the early evening to trick-or-treat, you can greet them with your telescope (and short ladder), a few fun targets to show, and a Jack O'Latern of treats to hand out. You can even tell them a bit about the astronomy tie-in.

Gibbous Moon
.

The best object to show on Halloween 2014 is the Moon. With an 8.4-da- old waxing gibbous phase, its light will dominate the sky to the south. But it is also a very easy object for first-time viewers to appreciate through a telescope. Bright and intuitively easy to relate to, what you see in a low power view are its dark seas and big craters. These will be seen both through the telescope and looking up at the moon with the unaided eye.

Low Power Telescope View
.

The Moon will be high in the south as darkness deepens. Here you can see what the Moon will appear like in a low power view. Most obvious will be three huge mares, or seas; the dark areas on the upper half of the moon.

Half The Moon Is Sea
.

The largest sea is Mare Tranquillitatis, close to the lunar equator. Above and attached to it is Mare Serenitatis, appearing more circular. Toward the limb of the moon, above the eastern edge of the big mare, is Mare Crisium, the Sea of Crisis. It is very round, very dark, and distinct. All three are lava-filled basins. You can also get some nice views of half of Mare Imbrium high up next to Mare Serenitatis, along the shadow line, or terminator.

Half The Moon Is Crater
.

In contrast to the northern half, the southern visible portion tonight is pock-marked with craters. Scan around with your telescope, particularly near the south pole along the terminator for high contrast views of shadow and light inside the larger craters.

I mentioned Halloween has an astronomical history. So here's the story you can tell:

The celebration of Halloween dates our distant ancestry, and across cultures. Its astronomical tie-in has to do with recurring annual dates. Most of us know the four major time demarcations each year; vernal equinox where (northern hemisphere) day becomes longer than night, summer solstice; the most daylight of the year, autumnal equinox when night becomes longer than day, and winter solstice with longest night of the year. Between each of these is a half-way mark, called a "cross-quarter day."

Halloween historically fell on a cross-quarter day, the actual day being Nov. 7. It was the Scots and Irish celebrating it as "Samhain", between years 1,000 and 1,200, when the Pleiades star cluster would transit overhead at midnight. Samhain was a celebration of the deceased, the ghosts. At Samhain, the ghosts would leave for the season, going to their rest. Over many years this celebration became All Hallow's Eve, or Halloween, A cross-quarter day with a ghostly theme, halfway between the autumnal equinox and winter solstice. In Central American culture, friends and relatives are remembered in Día de Los Muertos, or Day Of The Dead. It is the same celebration!

Other astronomical objects have a Halloween theme as well. They tend to be almost nebulae, as clouds of gas and dust, and we make shapes in their dark and light tones.

The Soul Nebula
.

Two difficult ones visually are the Soul Nebula and Witch's Head. The soul is ghostly in shape.

Witch Head Nebula
.

The Witch's Head really looks like its namesake!

There are two ghosts in the night sky! Can you name them? One is named because in early telescopes little detail could be seen, and these type of mysterious objects (planetary nebulae) looked like round planets. One of the ghosts appeared like the planet Jupiter. It is a spring object, so not visible this time of year. The other ghost is little, looks like a small "smoke circle" when viewed in amateur telescopes, and is setting in the evening with the constellation Ophiuchus. Can you name these planetary nebulae ghosts?

What would Halloween be without creepy spiders? The Red Spider Nebula and Tarantula Nebula are perfect for this night! The red spider may be viewed in amateur telescopes, but not much detail can be discerned. In comparison, The Tarantula is a treasure trove of complex nebulae for observer in the southern hemisphere.

Cat's Eye Nebula
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Ghosts, spiders, witches, what more could there be? The Snake Nebula is a dark nebula, part of a gigantic complex of dust toward the center of our home Milky Way Galaxy. It is a treat to see it in telescopes from a dark sky. The Owl Nebula fits our Halloween theme, as a creature of the night, and so does Cat's Eye Nebula in Draco, a fine sight in amateur telescopes.

The Medusa Nebula is large and dim, currently visible in Gemini in the morning sky. This is a large and dim planetary nebula, and very challenging to observe. But knowing what happens to humans seeing the Medusa, perhaps its better to just enjoy knowing its there.

With so many scary Halloween themed creatures in the sky we should feel fortunate to have the moon tonight, as some easy and even friendly "eye candy" to show visitors.

Get your telescope out in the early evening and share some treats. You might even consider handing out Milky Way and Mars bars.

Happy Halloween!

Mark Wagner

All maps are courtesy Virtual Moon Atlas. Photos are courtesy of NASA.

In a previous Telescope.com article, I gave a list of essential items needed to do urban/sidewalk astronomy. The list is good for any astronomy observing outreach, but best suited for light-polluted urban settings using a "public hands-on" approach.

So now you're ready to head out to the restaurant or pub patio, the coffee shop veranda, or just out on the sidewalk. What do you look at? City and business lighting may make it tough to see many stars in the sky. But really, all you need are two or three good things to view, and often there can be even more. Here's a list of the best objects to view from city locations:

First Quarter Moon through an XT8 Dobsonian, at Orion's last star party. Credit: Maria Grusauskas

1. The MOON: This is an easy, obvious target if it's the right phase-anything from about three days after New Moon to sometime around Last Quarter. While the Moon is hated by those hunting deep sky objects at a dark site, it's the object everyone wants to see in an urban setting. Binoculars are good for panoramas, especially if there are nearby trees and thin scattered clouds you can put in the FOV. The most modest scope can show amazing detail on the surface. It just blows people away, especially the craters-I'm always amazed they're so amazed by that. In larger phases, an adjustable polarizing filter can be a good thing to cut down the glare. I prefer using a wide-field eyepiece rather than tight-in magnification, so folks can track and follow easier when they run the scope-which I always encourage.

2. SATURN: The next-most-impressive object to the Moon. With a little scale on it, people will accuse you of pasting a picture in the scope. This is a good time to show them (if you're using a reflector) that there's just a mirror at the bottom and a small mirror at the top, bouncing light right into their eye-no tricks! They'll be especially impressed by any moons visible, and Titan, at least, almost always is. Like all objects, have a "cheat sheet" in hand or in your head with some basic facts, like size, distance, and number of moons. Depending on your scope, maybe a little more magnification is in order, but not TOO much: you want to make sure it's easy to track.

3. JUPITER: The "other" impressive target. Cloud bands and the Galilean moons are always visible unless conditions are terrible. People love watching the moons move around through the evening, and they're amazed that they can be spotted even with binoculars. This is a great object to show through both the binos and your scope. Thick haze can ruin it, though, so wait it out or pack it in! If at a tavern, and you're a bit of a gambler, an entertaining "wager" can be to see if your patron can name any or all of the Galilean moons. Don't believe they never can-I've lost this bet before, requiring all four. Pay up if you lose! As always, know which moon is which: this is very easy to do with any number of apps, tweets and sites which will keep you informed. Jupiter's Great Red Spot is not often visible from urban settings, even if face-on. But it's good to know when it is anyway, because someone will ask. And who knows, maybe you will be able to see it.

4. The SUN: There is no more-impressive object than our closest star. Obviously exclusively a daytime target, this requires a white-light solar filter or a hydrogen-alpha scope. It's a stand-alone target for daytime outreach, other than the Moon or Venus, which can sometimes be seen depending on their location in the sky. The H-alpha scope is by far the best way to go, as most people have never seen this view at all unless it's in a photo in a magazine or online. All you need is a clear day, the time and inclination to do it! This is THE target for daytime festivals and public events. It's also the one where I tend to do the aiming, rather than allowing the patron to do so, since it's tougher than aiming a Dob, and the H-alpha scope tends to be a little more fragile and pricey.

5. ORION'S SWORD/ORION NEBULA: For a light-polluted place, Orion's entire Sword through astronomical binoculars is the better of this pair of targets. While the Sword is probably visible naked-eye, the amount of stars, and the small view of the Orion Nebula in the middle, is a very easy and impressive sight from all but very bright places. If it's a bit darker, the Orion Nebula through a scope can be very good as well, but often it's not; it'll never look like that OIII filter view from your dark site. But I've had a viewer be able to see the four main Trapezium stars from a tavern patio; not bad!

6. PLEIADES: This is a real crowd-pleaser through binoculars, and of course too large to fit into any but a rich-field scope. People can see it in the sky, although they may have to shield their eyes from nearby lights. And the view in binoculars is simply stunning. It's a challenge to see how many stars they can see naked-eye (I can usually only manage five myself) versus the binocular view (generally over thirty if they take their time). And the various names of this object are of great interest to most: many have heard of the Seven Sisters if they haven't heard of the Pleiades, but most have NOT heard its name "Subaru", and are pleased to finally learn why those cars have those stars in the logo.

7. ALBERIO: A good object, easy to find at the right time of year, and wonderful for showing color to those who wish to see some. Many are disappointed by the lack of color in images, having imagined the view through a scope is like a picture in a magazine. This is great for showing color due to its blue and yellowish components. And it allows some conversation about the Milky Way, (which probably is not visible from the city), and the "Northern Cross", Cygnus.

8. BEEHIVE CLUSTER: Much like the Pleiades, this is an extremely pleasing binocular object. Often viewers will want the scope aimed at these clusters as well, and that's fine-they can steer around and see more detail, but they'll get a very visceral lesson in object size. That can lead to a great conversation on best viewing methods: naked-eye for meteors and aurora, binos for very large objects, scopes for objects from low-magnitude (large clusters, many nebulae) to high-mag (planets, planetary nebulae).

9. MARS (SOMETIMES): People always want to look at Mars, and sometimes it does look good; when it's close enough to Earth and your scope can give it enough scale. A lot of the time though, it's not very impressive. But when it is, and you can get enough magnification to make it worthwhile, folks can be extremely impressed to see a lighter polar cap and surface mottling. And it's always better than Neptune or Uranus, and someone cracking wise will always ask to see the latter.

10. HYADES: More huge star-cluster fodder for binoculars. Easy to spot via Aldebaran in proximity to Orion and the Pleiades, your viewers can be very impressed by the number of stars and the amount of sky it covers. I'm going to throw in the northern Perseus star fields as well, when they're visible, and also scanning many areas of the summer Milky Way.

Credit: Barstronomy

BONUS OBJECTS: The International Space Station and Iridium Flares. www.heavens-above.com is a great place to find out when and where, although it's not the only site doing this. And even though the ISS is just a bright white light slowly crossing the sky on a good day, people LOVE to see it. However, it's generally too hard for people to track successfully, although it shows structure in large binoculars and a scope. You can let them try if you wish. The brighter Iridium flares are impressive due to their predictability and the fact that they happen frequently, about two to four times per night; people are pleased to find out they can learn easily when and where they'll be visible. Then, they can impress the neighbors by saying "the aliens are going to signal me from this part of the sky at such-and-such a time tonight." New respect in the hood!

BELIEVE IT OR NOT, PROBABLY NOT: The next objects are usually NOT very much to look at from an urban setting in a scope 8" or less. You might think they'd be, but in my experience I've mostly given up on them. For a darker site, certainly; light-polluted urban site, not really, but they are worth a try. Your mileage may vary, depending on your scope and the exact conditions from your viewing stage.

M13, Lagoon Nebula, Swan Nebula, Andromeda Galaxy, M81/82, Leo Triplet, Comets, unless they're quite bright, say 5th magnitude at least.

If you've got an obvious object I missed in this list, please let us know in the comments. Hey, I'm not a scientist-I just play one on bar patios! Until next time, eyes to the skies!

CAUTION: Never look at the Sun, either directly or through a telescope or binocular, without a professionally made protective solar filter installed that completely covers the front of the instrument, or permanent eye damage could result. When using a truss tube telescope to view the Sun, both a properly fitting solar filter and light shroud are required.

Now that summer is arriving to the northern hemisphere, we are about to enter the best time of year to see and photograph the most beautiful part of our own Milky Way Galaxy. Not only are there millions of stars and some amazing dust lanes in the band of the Milky Way, there are also a host of Messier and NGC objects as well.

What equipment will I need?

1. A camera with a large sensor, such as a DSLR or Micro Four Thirds camera. The sensor on most point-and-shoot cameras just isn't big enough to capture enough light at night to make photographing the Milky Way a worthwhile endeavor.


2. A wide angle lens with a large aperture. The summer Milky Way encompasses a lot of the night sky, so you will want to shoot with a very wide field of view. I suggest at least 24mm or wider, with an aperture of at least f/2.8. You can still get decent results with smaller aperture lenses, but the goal is to try and get as much light into the camera as possible without too long of an exposure.


3. A remote shutter release, or an in-camera timer option. Pressing the shutter with your finger causes camera shake, which can result in blurry images when shooting long exposures. See if there is an available remote shutter control for your camera. If not, most cameras have some kind of timer option. That way you can press the shutter button normally with your finger, but the camera will wait for a period of time before it actually opens the shutter. This allows the camera to stop shaking before taking the photo. A remote shutter release is the preferred option because it will also allow you to take exposures for several minutes in length if you are able to use a tracking device for even longer exposures. You will use the bulb setting on your camera and the remote to open and close the shutter.


4. A good sturdy tripod. You don't want the wind to blow your tripod over with your nice camera on it. You also don't want a light breeze to shake your camera during a long exposure and cause blurry images. I would recommend a tripod with a weight rating of at least 5 pounds. Orion sells three tripods that meet this requirement.


5. A couple of reliable memory cards with at least 16 gigabytes of storage each. You're probably going to be shooting a lot of images as you will likely have to experiment a good bit initially with your camera settings. I also recommend that you shoot with your camera in RAW mode so that you can have more control over processing them. Shooting in RAW mode comes at a price, however. The individual images will be much larger than if you were shooting in JPG mode.


6. A fully charged camera battery and at least one fully charged backup battery. Or, you can use a field battery and adapter, like Orion's Dynamo battery and DSLR adapter (compatible with Canon cameras). It is an awful feeling to be out shooting something really beautiful and having your camera die because of battery power. Get charged up ahead of time!

Now that you have your materials list down, here are some other details you'll want to consider before you set out to shoot the Milky Way:

1. You will of course want to find a location with dark skies. Light pollution is your enemy (and that includes the Moon). If you can't see any part of the Milky Way with your naked eye, then photographing it will be quite difficult. Get away from the city lights! Hopefully there is a national or state park with reasonably dark skies within a manageable driving distance.


2. Keep an eye on the weather. You will want to consult the Clear Sky Chart website for this.


3. Learn the phases of the Moon. The Moon is beautiful, but it interferes with our trying to shoot the Milky Way. Try to plan your shooting as close to the New Moon as possible so it won't interfere.


4. Know what time the Milky Way will rise so you can maximize your shooting time. A good piece of free software that can help is Stellarium. This program shows you what will be in the sky at any time you'd like to know about.


5. You will have to use both manual focus and manual exposure settings with your lens and camera. Automatic focusing and exposure will simply not give good results for shooting at night.


6. For manual focusing, set your lens to infinity focus mode if available. If not, try to focus on the brightest star or planet in the sky. Vega is a really bright star that is right next to the Milky Way. It might take you several test shots to get the focus exactly correct, so be patient and if your camera has a zoom feature which allows you to view your images that can be very helpful for focusing.

Getting Started with Camera Settings

1. Use the largest aperture your lens will allow.


2. Start with your ISO at 3200.


3. Set your exposure time to 20 seconds.


4. Review your image in the camera. If it's too bright, then lower the ISO and/or exposure time. If you don't see much detail, try raising them a bit.


5. You might find that setting the ISO too high will result in noise (or graininess) in your photos. Some cameras handle high ISO better than others; so take lots of test shots. Some noise can be reduced in post-processing.


6. Be careful of star trailing. Because the Earth is rotating, the stars appear to move across the night sky. This will affect your exposure times. The wider your lens is, the longer you can shoot without star trails. This article from David Kingham talks about the "Rule of 500" and how to avoid star trails.

Other Suggestions for Shooting the Milky Way:

1. Consider shooting with something interesting in the foreground. Trees, mountains, a lake, or any scenery you choose can add some real visual interest to your photos.




Image Credit: Stephen Rahn
2. Once you've gotten comfortable with shooting exposures of no more than 30 seconds, consider purchasing a tracking device that will allow you to take exposures that are several minutes long. The Orion StarBlast AutoTracker Altazimuth Mount will allow you to attach your camera so you can take much longer exposures. This will allow you to take photos with better detail and also reduce your ISO so you will have less noise in your photos.


3. Combine several images for a panorama or mosaic. You can use a program like the free Microsoft Image Composite Editor to combine multiple images into one larger one.


4. Use an intervalometer to create a time-lapse or extended star trails image. An intervalometer allows you to program your camera to take a series of exposures without your having to do anything. If you have a Canon camera, a free piece of software called Magic Lantern can do this for you without having to purchase a separate piece of hardware.


5. Learn from others. There are astrophotography groups on places like Flickr and Google+. Most people will provide assistance and suggestions if you ask nicely.



 

 

A successful night of astronomy outreach requires a few crucial ingredients to ensure both an awesome viewing experience for your viewers, a minimal amount of hassle for you, and the most fun for everybody!

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Here is a fantastic, tried-and-true list of what you'll need, compiled by Duke Skygawker, a professional astronomy outreach coordinator and founder of "Barstronomy" in Columbus, Ohio.

1. A scope you don't mind being manhandled:

A bare-bones 6" or 8" Dobsonian telescope works best, like an Orion 8" Classic Dob (or the old Coulter Odyssey 8 I use.) Just point and push. In bright areas, you'll only be looking at the brightest targets, almost all seen naked-eye (with a handful of exceptions). Let the viewer, with a little help, do aiming and tracking. Be prepared for fumbling on their part, but most pick it up quickly. Let your participants get their hands on the scope to help them get over the fear of "ruining expensive equipment." You'll teach them quickly that a decent largish scope is not that expensive or difficult to use!

2. An inexpensive wide field eyepiece or two:

Leave your high-end eyepieces (and worry) at home. When doing astronomy outreach, your EPs will be used roughly, guaranteed. I suggest something like a GSO Superwide 20mm, which gives a great view of the Moon and a decent view of Saturn and Jupiter. If you need to bump up power a little, use a superwide 15mm or 12mm. Not tack-sharp FOVs edge-to-edge, but the wide view is what counts. Orion Sirius Plossl eyepieces are a little bit more expensive, but offer great views. Use high powers not at all or sparingly - make it easy for your patrons to track the target.

3. A unity finder with a bullseye reticle:

No finder scopes. Use an Orion EZ Finder Deluxe II or the venerable Telrad. They love it because it's like aiming a big gun barrel and putting the bull's eye on the target!

4. Binoculars on a tripod:

I recommend using inexpensive astronomy binos - I use 20x80's. Whatever tripod you use, consider strapping it to a patio rail or other object if you can, just to deter accidents. Binoculars excel for the Moon with clouds passing in front, and larger star groupings like Orion's Sword or the Pleiades. Bonus: Everyone already knows how to use them, and finds they already have astronomy-appropriate optics at home in many cases. It also keeps people busy while they wait for views through the bigger scope.

5. Signage:

Especially if you are using a dobsonian telescope, some people won't know that cannon-shaped object is a telescope, since they have a mental image of traditional refractors. A large sign or banner tacked to the wall or fence, or even stuck on your telescope will clue them in. You can tell them it's a T-shirt cannon if you want; I like to say it's a "reverse photon cannon." Have a sign that tells what you're viewing. You can print these on 8x11 paper at home, but if you re-use them much, laminate them before use.

6. A small star atlas and a planisphere:

Inexpensive, useful, and easy to show people. You may not actually need them for finding targets at your event, but they are valuable examples of what to buy to be able to navigate the sky at home. The Orion Star Target is a good planisphere, and in my opinion, the S&T Pocket Sky Atlas is the best small atlas available.

7. An adjustable stool:

It's always more comfortable to sit and view, although some won't want to do so. I'm a huge fan of the common "Airlift" hydraulic bar stool for outreach events or for taking on dark-sky trips. Though it doesn't transport flat, it's lightweight, easy to pack around, and looks great, all for about forty bucks. Trust me, you'll LOVE it. If you don't sit on it, it's also a small table!

8. Knowledge:

Stored in your brain, or on a "cheat sheet" or card. In some cases (like solar H-alpha scopes, if daytime), a small sheet posted or handed out, explaining what people will see at the EP, can spare you repeated explanations, saving your voice and perhaps sanity. The planisphere and small star atlas you brought belong count in this category as well.

9. Appropriate attire:

No-brainer, right? Dress for your locale and event as well as the weather. If you're going to be bringing your telescope to a bluegrass festival, don't wear a tux, and don't wear a swimsuit to a wedding. Your star-studded beanie might not fit at a corporate mixer, but your knit-hat-with-built-in-dreads might be perfect at a reggae festival. And as an astronomer already, you already know to dress in layers for the expected low temperature, minus 20 degrees F or so.

10. A sense of humor and an even keel:

If you have fun, so will they. We all know a few astronomy jokes, but make them appropriate for the setting. "Your world is spinning" has applicability where adult beverages are offered. "Heavenly bodies our specialty" can be good for some crowds. "Nothing's stupider than Jupiter" just sounds funny, even though it's far from true. I've kept informal track of how quickly after beginning someone will make the standard joke about the seventh planet. Record: 17 seconds, and you may hear that multiple times in an evening. Grin and bear (not BARE) it! And, if it happens to be a night you find yourself in a foul mood, FAKE IT! You'll probably wind up having a good time anyway.

Orion suggests:

An eyepiece video camera is also a great tool for astronomy outreach, especially when you're dealing with large crowds. By projecting the eyepiece view onto a larger screen, more people will be able to see what's in the eyepiece without having to wait in line for their turn at the telescope. This is also an great tool to use when there are children present. Finally, at our last Star Party, many people were excited to be able to take pictures of the Moon with their cell phones. Having a SteadyPix adapter for cameras and smartphones really helped this process!

After some 47 years of observing, Roger Ivester finally purchased an Orion 1.25" Correct-Image Star Telescope Diagonal for his Orion 102mm Refractor. The precision 90 degree diagonal is meant to deliver superior image fidelity, or a right-side-up, non-reversed image. Ivester, who observes visually and sketches through the eyepiece on a regular basis, was pleased with results. His full review is as follows:

I love to observe with my 102mm refractor, but I don't like the reversed mirror image view presented, due to the 90 degree diagonal. On many occasions I choose my Newtonian, as it's so easy to make a correctly oriented pencil sketch. For many years, I've wanted to try a correct image 90 degree diagonal, but thought the views might suffer. I've been using a 96% enhanced reflectivity mirror diagonal for many years.

The reason I dislike making a sketch using a mirror image reversed view is that almost all published images and sketches are oriented scientifically correct with N at the top and W to the right. It's also very easy to confuse the cardinal points with a standard view diagonal, when making a sketch or noting a faint feature of the object being observed.

One thing I should mention. A correct image prism diagonal such as this Orion, also known as an Amici: When observing a very bright star with any correct image diagonal will show a very thin thread of light crossing from edge to edge. This is not a defect, but is inherent to this type of diagonal. I only noticed it when observing Sirius, and found it not to be objectionable. I purchased this diagonal, not to observe the brightest of stars, but to observe the faintest of deep-sky objects possible with a 102 mm refractor.

I plan on much more observing, notes and sketching with my trusty 17-year-old Orion 102mm refractor. Again...I love a correct image view, and sketching with my refractor will never be the same again. I'm very happy with my new purchase.

While looking through the Orion Telescopes & Binoculars catalog last week, I noticed a 1.25-inch, correct image diagonal. After many years of wondering how this type of diagonal would perform, I picked up the phone and ordered one. After all, Orion has a fabulous return policy, should it not meet my satisfaction. I had nothing to lose...

Within just a few days, my diagonal arrived. I could hardly wait to give it a try. On March 5th, 2014, I set up my Orion 102mm refractor for the big test. I started with a very high magnification of 200x, to examine the Trapezium stars and see how the view would compare with my current enhanced mirror diagonal. The stars were beautiful in both, and even the "E" star could be glimpsed. First test: passed. I then went to my favorite galaxy pair, M81 and M82 at 57x. I immediately loved the non-reversed and correct image view of these two beautiful galaxies using my new diagonal. I really couldn't see any difference between the qualities of view. The next test would be Jupiter, and again both diagonals presented fabulous views. The cloud bands appeared very sharp with an incredible amount of detail visible.

It is my opinion, the correct-image Orion image diagonal, catalog #8787 seemingly passed all tests with flying colors. At this point, I put my beautiful enhanced solid aluminum mirror image diagonal in my eyepiece box, where it will probably stay. For the remainder of the evening I enjoyed using only my new "correct image" diagonal.

I can hardly wait to start sketching with my new refractor accessory. I just wish that I had made this purchase many years ago.

Read more of Roger's astronomy blogs and see his sketches at www.rogerivester.com.

As spring begins, Leo is transiting due south in the early evenings, and presents us with some interesting bright, and not so bright, galaxy groupings. These can, for the most part, be viewed from a reasonably dark sky, in instruments as small as four inches. Of course, some will require larger optics, but that should serve to interest you in joining other amateur astronomers observing, getting away from light polluted skies, and seeing just what there is to see. Let's begin.

The image above shows our early April sky, two hours after sunset. Looking mostly south-southeast, you'll find bright star Spica in Virgo. Above it to the south is the constellation Leo, marked by its brighest start, Regulus, which anchors the Sickle asterism. In The Sickle is the fine double star Algieba. Leo's back haunches are punctuated by the star Denobola. We will use these stars to locate three galaxy groups.

The Leo Trio or Leo Triplet, located near the "rear" of Leo. This grouping comprises three well known galaxies; two of which were bright enough to come to the attention of French comet hunter Charles Messier in 1780. The third member, NGC 3628 was discovered by famed observer Sir William Herschel in 1784. Here is where you'll find them, one bright star back from Denebola, and down:

M66 is the brightest at magnitude 8.9, 36 million light years from us. M65 shines at magnitude 10.25, and along with NGC 3628 is 35 million light years from us. The three are gravitationally bound - as evidenced by their proximity to each other and distance from us. NGC 3628 is a challenge object at magnitude 10.26, appearing dimmer due to its large angular size - and to my tastes the most interesting due to its distorted appearance.

In deep images of the group, NGC 3628 shows a tidal tail about 300,000 light years in length. This is material streaming out of the galaxy as it moves through space, presumably the result of gravitational interaction with the two other members of the group. Here are images of the three together, courtesy of NOAO:

Can you tell which is which based on what you've read, and why NGC 3628 has been nicknamed "The Hamburger"?

Let's move to the next group in Leo - M95, M96 and M105.

Located just below and a bit over two-thirds along a line described from Regulus and the star used to hop down to the Leo Trio, this group of three galaxies - M105, M95 and M96 (the M96 group) is visible in a single binocular field of view.

All three galaxies are in the 10th magnitude range, varying in distance from 31 million to 36 million light years from us. The group also includes a few dimmer members surrounding M105. M95 and M96 were discovered by Charles Messier's protégé, Pierre Méchain, in 1781. M105 was added to the Messier catalog by Helen S. Hoag, after she found reference to it in a letter from Méchain referencing it. Here is how they look in a single image:

M95 is at the lower right, with M96 to its left. M105 is the roundish glow upper left, and nearly as bright is NGC 3384 - the elongated glow to its left. NGC 3389 will be the challenge object of the group, significantly dimmer at mag 12.4. The Messier members of this group will all be visible in a 4 inch telescope, as I expect NGC 3384 will be as well. NGC 3389 has been reported visible in a six inch telescope - maybe you'll give it a try in something smaller and let me know if you find it. Image is courtesy SEDS, Arizona.

The third grouping is an esoteric one. NGC 3226 and NGC 3227 are a pair of brighter galaxies with dimmer ones in the same field of view. The brighter pair are part of astronomer Halton Arp's Atlas of Peculiar Galaxies. NGC 3226 is a dwarf galaxy, paired and interacting with the spiral galaxy NGC 3227. These are very easy to find - next to the beautiful double star Algieba (Gamma Leonis), which you should pay a visit to on your way to these galaxies.

Here is how the pairing appears, although it will not appear photographic in your telescope like this image:

I've read one report of viewing the brighter pair in a 102mm telescope, but all other reports are in 8 inch or lager instruments. NGC 3227 is almost 66 million light years distant, and shines at magnitude 11.28. NGC 3226 is 70 million light years from us, shining at magnitude 12.3. If you can pick up those two, try for NGC 3222 - dim at mag 13.7, and an amazing 232 million light years away.

Want more? Here's the tough one: CGCG 94-22 (Catalog of Galaxies and Galaxy Clusters) is a tiny speck, a multiple galaxy system, shining at magnitude 15.4. This pair of galaxies is 595 million light years from us! Thanks to Bob Frankel for this beautiful image showing the tidal interaction between the large galaxies, and even hints of such in the tiny pair. You can easily see the "dance" the galaxies have been doing together by the trails of material around them. If you're wondering what the rays are from the right side of the image, it's the brilliant double star Algieba. Here is the original image on Bob's website.

I'm eager to hear from some of you who try hunting for any or all of these targets. The brightest members offer quite a bit of detail. I personally love The Hamburger, as it is visible without much work, and is an unusual target. The dimmer stuff? well, icing on the celestial cake.

Going galaxy hunting in Leo? Come back and leave a review of this article, and let us know what you used to find them, and which was your favorite.

Clear skies,

Mark

During the totality phase of a total lunar eclipse, the Moon is completely immersed in Earth's shadow. If you were lucky enough to be standing on the Moon during totality, the Earth would be completely dark, with a ring of sunshine around it. "And this brilliant ring would be bright enough to dimly light up the lunar landscape," says Alan MacRobert of Sky and Telescope magazine.

But, we're not on the Moon, at least at the time of writing this. And from Earth, what we see during a total lunar eclipse is a little less predictable, which kind of makes the whole thing even more exciting, and worth staying awake for.

Total Lunar Eclipse Montage, by Justin Van H.

While mainstream media usually buzzes with the promise of a "Blood Moon" before a total lunar eclipse, Michael E. Bakich, of Astronomy magazine is a little more real about it: the Moon's appearance during totality can vary greatly from one eclipse to the next, he says.

So while we all hope for a bright red Moon ? the result of shorter blue rays of light being scattered from the Sun rays which bend through our atmosphere and across the Moon's shadowed surface ? it's only one of several different possible outcomes. Variables that affect the Moon's appearance include the path the Moon takes through the Earth's umbra, which is not always completely centered, and the state of the Earth's atmosphere, which contains water droplets and solid particles like dust and ash, which reduce the air's transparency, says Bakich.

"A significant volcanic eruption before a lunar eclipse can darkest the Moon's face considerably by pumping our atmosphere full of particles that halt light. Lots of clouds along the edge of our planet also can cut down the light," writes Bakich in the April 2014 issue of Astronomy. You can see an example of this by googling pictures of the total lunar eclipse of December 9, 1992, which occurred just months after Mount Pinatubo blew in the Philippines.

In the time leading up to a total lunar eclipse, all we can do really is make a few predictions, get our telescopes, binoculars, cameras, and eyeballs ready, and wait. Bring your observing notebook outside too, so you can take notes about the characteristics of this particular eclipse.

How to Estimate the Luminosity of a Total Lunar Eclipse:

In 1921, the French astronomer André-Louis Danjon created a five-point scale for estimating the darkness of a total lunar eclipse. The L value stands for various luminosities, starting with the darkest. Below is a chart of Danjon's system, as explained by Bakich:

"In evaluating L, you should record both the instrument you used (if any) and the time," says Bakich. "Also document any variations in the color and brightness of different parts of the shadow, as well as the sharpness of its edge. Pay attention to the visibility of lunar features within the umbra. Notes and sketches made during the eclipse will help you recall details later."

As far as estimating the darkness and color a total lunar eclipse, Bakich recommends notes as opposed to images, since cameras typically record more than the eye can see, and often vary.

The Full Moon of April falls on the 15th of the month. As we look forward to the total lunar eclipse on the night of the 14th-15th, let's observe the Moon before it's completely full. After all, the best time to observe the Moon is when there is still a line of shadow falling across it. On Saturday, April 12, the Moon is waxing gibbous at 12.68 days old, and 95% illuminated.

The Moon is ever changing, and even the special features we tend to visit over and over take on new and interesting appearances, as the shadow line, named the Terminator, moves minute by minute. Here is our Moon as of Saturday, with a few interesting targets identified for you to observe:

Below are detailed images and description of those areas. These are fun to view in a telescope under good conditions. I've heard people say the view feels like flying over the lunar surface!

Grimaldi is visible in 10 power binoculars. It is a very dark circular formation, appearing much like a sea, or Mare. You may see a number of small craters on its very flat and smooth floor, Grimaldi also has very high slopes, with pock-marked craters embedded in them. This is a great time to pick out details.

Hevelius is very close to Grimaldi, and forms a nice pair with Cavalerius just above it in this image. This crater too has steep slopes embedded with many small craters. The floor has a small central peak. See the cross-marks near the central peak? Those are part of Rimae Hevelius, rilles that criss-cross the floor. The main crater can give pleasing views in a 10 power binocular, but for details such as the rilles, you'll need something more like a 12" telescope.

Mons Rumker can be viewed in an instrument as small as a 50mm refractor, and is a pleasant surprise among lunar targets. It is described as a tortured area of lunar domes forming a circle, and showing steep slopes. I think it is an anomaly among lunar features. In the large Sinus Roris (Bay of Dew) surrounding it, you'll find other small isolated lunar domes as well ejecta rays from ancient impacts splayed across the surface.>

There is so much to explore on the Moon, and following the Terminator makes it all the more enjoyable, since it is the area of highest contrast between shadow and light. The features really pop out in 3D.

On tonight's map at the start of this article, I point out Porrima - Gamma Virginis. This is a wonderfully tight double star. During my years observing, it has gone from a 2.5 arc-second separation (1995) to 0.4 arc-second in 2008. In 2010 it was back to 0.9 arc-seconds and now is back to over 2 arc-seconds, and significantly easier. You can "split" this double star now in a 50mm telescope. It is a true binary star, where both members are bound together by gravity, shining individually at magnitudes 3.6 and 3.5. They shine at a combined magnitude 2.6, 39 light years distant, and have an orbital period (around their common center of gravity) of 169 years.

Gamma Virginis is a star you'll enjoy watching year after year - as you can watch the changes in separation.

Finally, here is an image from Starry Night Pro, of what Mars will look like tonight:

I considered describing its features (I love the Tharsis Montes craters lower right!) - but instead will refer you to the Mars Observing Guide already written on the Orion website, delineating the various features you should try to see.

Tonight is a great time to observe Mars, which is at its brightest. The good news is, even tonight's big Moon won't interfere with your views. Get your scope, family and friends out, because tonight is an observing delight!

Please leave a review on this article, and let me know what you observed in your telescope, and what features you were able to see.

Clear skies,

Mark Wagner

Images courtesy the Lunar and Planetary Institute From The Consolidated Lunar Atlas. Mars image from Starry Night Pro.

Duke Skygawker of Barstronomy writes about the public outreach he does with his dobsonian telescope 'Big Red' in the middle of Columbus, Ohio.

It's called Barstronomy because that's where it mostly takes place; at taverns and music venues with an outdoor area, in the middle of the city in Columbus, Ohio. It began in my neighborhood at Woodlands Tavern, where I'd been a frequent attendee and sometime performer at their Wednesday Open Mic. It began with a dare.

While at Woodlands Tavern, I naturally talked about my astronomy hobby, and it was only a matter of time before a friend dared me to bring my dobsonian telescope to the bar and set it up on the patio. When I did, the response was greater and more positive than I'd ever anticipated, and that led to the founding of Barstronomy.

Since that first night three years ago, Barstronomy has been featured at Rumba Cafe, Skully's Music-Diner, and Brothers Drake Meadery as well, all in Columbus. The outreach also covers community and music festivals and other public events. If you note some similarity with John Dobson's "sidewalk astronomy," you're paying attention! In the "sidewalk astronomy" concept, you take astronomy to the people, rather than making the people come to the astronomy. The people just happen to be where astronomy is happening. So I just took astronomy off Dobson's sidewalk and onto the bar patio, and was surprised by the enthusiastic response.

The Barstronomy dobsonian telescope on the Woodland Tavern in the middle of Columbus.

Of course, Barstronomy also participates in more "traditional" astronomy outreach, through my local club, the Columbus Astronomical Society, at their site, the Perkins Observatory in Delaware OH. I also do outreach at schools, libraries, parks, and community centers. That type of outreach is definitely more common, and can have great impact. For example, Perkins is a "real" observatory with a (very small) staff and a wonderful building and history, and these aspects of attendees' visits to a program add much to their experience and perception. Traditional astronomy outreach programs such as these are generally at a darker site than downtown, and the expectations of the public and the astronomers presenting are not the same as those encountering a telescope at a music event or pub, in ways I'll explore in a future entry.

Astronomy binoculars at a Barstronomy outreach event.

But getting out in person, in public, isn't the only way astronomy outreach happens. Books and other publications were the first written outreach form, and still figure prominently as outreach, but probably tend to reach mostly those already possessing interest in the subject. Written outreach has also evolved to include all things Internet and World Wide Web, including social media (like Twitter and Facebook), agency and observatory websites, club websites, and astronomy blogs.

NASA, magazines like Astronomy and Sky & Telescope, observatories, astronomy clubs and individuals (think Canadian astronaut Chris Hadfield, Neil deGrasse Tyson, and others) have all embraced this approach to get the word out and help popularize the beauty of looking at the sky. The goal of this outreach may come from an internal passion, but may also inspire a certain number of people to be more directly involved, either as a hobbyist, a professional astronomer, or simply as an informed advocate. Outreach isn't important to every amateur or professional astronomer. Some of them (you?) prefer to do your observing alone, at home, or only with a few fellow enthusiasts.

Tony Miller (Duke Skygawker) of Barstronomy, on the evening of the Venus Transit.

But somehow, something or someone reached out to you to get you started - a parent, a program, a class, or just a look up at the night sky when you were in a contemplative, receptive mood. And you reached out in response, with your curiosity and talent, to see what it was all about. That's outreach in its best form!

What does astronomy outreach mean to you? Share your thoughts in the Review section of this article.

The Great Orion Nebula, or M42, is a favorite of deep sky observers, particularly in the northern hemisphere. In terms of visually available details and beauty, its only competition is the Eta Carina Nebula, visible in the southern hemisphere. Given its brightness, wealth and range of detail and ease to locate and observe with instruments from small binoculars on up, this M42 is a true crowd pleaser.

Sky chart of M42's location on 4.1.14. Starry Night Pro

In this guide to the Great Orion Nebula, I'll describe some of its physical features and its surroundings, as well as some of the cosmic processes taking place that make it intellectually interesting, in addition to its tremendous visual beauty. Every fall I attend a star party with a large number of other observers. We go out during New Moon between mid September and mid October. At this time in the northern hemisphere, nights are getting longer and cooler, and the summer Milky Way is transiting, making way to deep sky views in the east. But the biggest treat always turns up just before dawn, when Orion rises over the horizon, telling us winter is approaching. It rises earlier and earlier as the season continues, dominating the sky come December and January, and slipping out of prime observing position around early April.

So, why look at it now, just after the spring equinox? Winter has passed, and so will this great object. It's time to say one last farewell to the magnificent Hunter, until he returns in late fall next year.

Located in the star forming arm of our galaxy, along the Milky Way, the closest arm of our galaxy, M42 is visible without optical aid as a fuzzy patch in Orion's sword, which is made up of the three prominent unaided-eye stars descend from Orion's belt stars.

This is a huge object: it sits 1344 light years from us, and its greater extent is several hundred light years. Thought to be 3 million years old, it is home to some of our galaxy's youngest, and hottest stars (much hotter than those in Hollywood).

M42, Credit: NOAO

When you view M42 with magnification in a telescope, you will certainly notice the four brightest, and hottest stars in the nebula - they are appropriately named the Trapezium, forming a very tight trapezoid. These stars are know as the A, B, C and D star. Seen in the image provided, they are the four brightest stars at the visible core of the nebula. On very good night, you can see a few other stars in the group; the E and F stars. While they all look bright in this image, the F star can be challenging, and E can be downright frustrating! But on a good night, when the air is steady, and you can increase magnification, all six members of this hot cluster will reveal themselves.

Look at the great sweeping arms of the nebula, outstretched like a birds wings. This is an area of dust that has been excavated by the stellar winds of the hot stars in the Trapezium.

Wide field M42 image courtesy of Wikipedia Commons

At times, observers may see varying hues of color in the bright nebula around the Trapezium, and in the arms. Reds, browns and green tints - not vibrant, but suggestions, hints of color. What colors do you see? The arms themselves look like sculpted clay - amazingly fine detailed textures. It is a stunningly beautiful view!

Look too, just behind the Trapezium, and you'll see an area as black as can be found in space. This is a molecular cloud of hydrogen and dust that forms an inky black dark nebula.

Trapezium, courtesy of JPL

It's the stuff that stars are made of, and The Trapezium stars are some of the results! If your eyes could see in infrared, through the dust of the Orion Nebula, you'd see thousands of young stars and proto-stars that are hidden to our eyes, deep within this stellar nursery.

While you're in the area, take note of the other great objects very close by. If these others were not located so close to the Great Orion Nebula, they'd be famous on their own: M43, looking like a comma adjacent to the dark nebula behind M42. Further still, but close by, are the reflection nebulae NGC 1973, and NGC 1975 and NGC 1977, which show well in a dark sky, and are collectively called The Running Man. You'll see wispy suggestions of star stuff enveloping several bright stars. Just to the other side of that is the Open Cluster NGC 1981. Lots to look at! But I'm sure you'll agree, the main attraction is M42.

Orion area chart from Megastar

As you let your eyes relax and take in the view, you'll feel like you begin to see more and more, picking up on dim nebulae extending out from the arms. Allowing your eyes to take it all in, you'll come away feeling like the true size of the nebula is twice what you thought. In truth, its hundreds of time the size you thought!

Since you know M42 is visible naked-eye, try a pair of binoculars on it. The nebula will be very obvious. If you have a telescope, and the bigger the better applies, there is a fantastic amount of detail to see. You'll come away knowing that, on those early fall mornings later this year, a treat awaits you! Maybe I'll view it with you at our star party here in California.

Let me know what you think of the Great Orion Nebula. Tell me some of your observations and send in drawings. We'll do our best to answer you and show some of your works!

Clear skies,

Mark Wagner

The sickle shape of Leo the Lion is easy to find in springtime skies, and it's a promising hunting ground for galaxies, with over 60 listed in The Millennium Atlas.

The challenging compact galaxy cluster, Hickson 44, also named the Leo Quartet, or Galaxy Cluster NGC 3190, after its brightest member, is located less than halfway between the stars Adhafera [Zeta Leonis] and Algieba [Gamma Leonis] along the sickle of Leo. (RA: 10h18m00.4s Dec:+21°48'44").

Paul Hickson defined a compact galaxy cluster as a "small, relatively isolated collection of four or five individual systems that are set in close proximity to one another, and that differ in brightness by no more than 3 magnitudes." Our challenge object is around 100 light years distant and consists of the four galaxies; NGC 3190, NGC 3193, NGC 3187, and NGC 3185. Two edge-on spiral galaxies are at its center; the dust lane-spliced NGC 3190, and S-shaped NGC 3187. NGC 3193 is an elliptical galaxy, and the face-on spiral galaxy NGC 3185 floats the farthest from the other three.

Image of NGC 3190 Galaxy Cluster by Jim Gianoulakis.

While this group of galaxies is evolving and interacting together across vast distances, you can collect them in one eyepiece view. But, they are by no means easy, says Tammy Plotner, who recommends a minimum of 150mm telescope to see them under dark, clear skies.

Recent observations and sketches by notable observers:

Roger Ivester of North Carolina:

The following observations were made using a 10-inch f/4.5 reflector, from a fairly dark site in the South Mountains of western North Carolina. The accompanying sketch was made at a magnification of 114x, with a 0.50º field of view.

At magnitude 11.0, NGC 3190 is the most prominent and most easily recognized member. This galaxy is bright, highly elongated, and oriented NW-SE. It also has a brighter elongated core.

NGC 3193 at magnitude 10.9, appears fairly small, round and highly concentrated in the middle. With higher magnification, a stellar nucleus can be seen.

NGC 3187 is the faintest of the group at mag. 13.1, and can be very difficult. It is located about 5 arc minutes NW of NGC 3190. This small and very faint galaxy is highly diffuse without concentration. On nights of less than excellent transparency, this galaxy is not visible with the 10-inch. A challenge for sure, and averted vision is mostly always required for me, and seldom can I hold this faint galaxy constantly.

NGC 3185 is faint at magnitude 12.2, and lies about 15 arc minutes SW of NGC 3190. The shape is mostly round, appearing as a very diffuse subtle glow, but fairly easy to see.

Jaakko Saloranta, of Finland:

Hickson galaxy clusters are generally considered to be objects for larger apertures but several of the galaxy clusters can be seen even with small telescopes. A good example is Hickson 44 - the second brightest of all the Hicksons - in which all of the member galaxies are brighter than 13.5 magnitude. This makes the two brightest members (NGC 3190 & NGC 3193) fairly easy targets for small apertures and the two fainter ones (NGC 3185 and especially NGC 3187) a great challenge for any telescope.

With a cheap 3 inch (80 mm) refractor I was able to see three of the four members from under a fairly dark location at the Teide caldera in Canary Islands (Spain) from an altitude of 7480 feet (2280 meters). The brightest member in the group - NGC 3190 appears as a fairly bright, elliptical 3' x 1' disk with a brighter nucleus. NGC 3193 an even brightness, round glow close to a 9th magnitude star. NGC 3185 appears only as a very faint, very small and slightly elliptical streak of light without details. With an 8 inch Orion DSE, all four of the members are visible at 96x under mediocre skies, although NGC 3187 remains very elusive.

Fred Rayworth, of Las Vegas, Nevada:

From the desert SW, using a 16-inch f/6.4 at 70X, the four galaxies were easily seen as variously shaped smudges. NGC 3190 is a fairly bright oval smudge right in the middle of the group, mostly featureless. Just a bit NE, and next to a relatively bright star is NGC 3193, a slightly brighter ball of light. It reminded me of an unresolved globular. WSW lies NGC 3185, appearing as a soft, mostly round glow. The most difficult of the group is NGC 3187 at mag. 13.0 and is by far the most difficult of the group. It lies just a few minutes, NNW of NGC 3190. By far the hardest one to see is NGC 3187. All four galaxies fit nicely in a 1/2º field of view.

Interested in contributing your observations to the next Deep Sky Challenge? Email mariag@telescope.com.

More to The Picture: The Cave Nebula

If glancing at this image takes your attention immediately, it should. Not only is it ethereally beautiful and aesthetically pleasing, it's shrouded in bizarre cosmological coincidences. We see a dazzling array of multi-colored stars, but within this single area of space is a hidden ancient planetary nebula, a reflection nebula, a dark dust cloud, a Bok globule, a peculiar low-mass protostar, the edges of a massive X-ray bubble and the fringes of a supernova remnant. Hold on to the light of the Cepheus Flare and let's step inside Wolf's Cave...

Cave Nebula, by Orion Staff. Full details here.

In the northern fringe of Cepheus lay an enigmatic gathering of cosmic dust clouds that first gained the attention of astronomers in 1908 when Max Wolf and August Kopff first noticed its complex structure. Using a 28-inch reflector, Wolf took a 2.5 hour exposure of the dusty area which he described as a "long, dark lacuna" and positively identified the reflection nebula cataloged as Sh2-155. His assistant, Kopff, using the same photographic plate, was the first to note the Bok globule which later became cataloged by E.E. Barnard as B175.

Those were wonderful years for astronomy; years when poetic descriptions were still acceptable to the general consensus, and Wolf dubbed the area the "Cave Nebula." But this isn't a spelunker's dream, because the radiation emitted from the nearby bright, young OB star would obliterate any explorer into this thick knot of interstellar dust. But there was one traveler, who dared: a main sequence star whose course took it through the dust maul at nearly 12 km per second. Running headlong into the obscuring mass at nearly supersonic speeds, the star slammed into Bok globule B175, sending shockwaves rippling through the structure and producing collisional excitation and ultraviolet pumping. The result of this cosmic crash was, of course, noted by Wolf in 1908 on his photographic records, but it was while searching high above the Milky Way's galactic plane in 1934 that this dusty molecular cloud was spied by Edwin Hubble and became known as the Cepheus Flare.

Together, reflection nebula Cederblad 201 and Bok globule B175 are referred to as van den Berg 152, and sometimes called Lynds Bright Nebula 524. Yet, it is Cederblad 201 itself that so interests modern science. Why? According to studies done by Goicoechea (et al) with the Spitzer Space Telescope, "We present the detection and characterization of a peculiar low-mass protostar (IRAS 22129+7000) located 0.4 pc from the Cederblad 201. The cold circumstellar envelope surrounding the object has been mapped through its 1.2 mm dust continuum emission with IRAM 30 m/MAMBO. The deeply embedded protostar is clearly detected with Spitzer. Given the large near- and mid-IR excess in its spectral energy distribution, but large submillimeter-to-bolometric luminosity ratio (it) must be a transition Class 0/I source and/or a multiple stellar system. Targeted observations of several molecular lines from CO, 13CO, C18O, HCO+, and DCO+ have been obtained. The presence of a collimated molecular outflow mapped with the CSO telescope in the CO line suggests that the protostar/disk system is still accreting material from its natal envelope. Indeed, optically thick line profiles from high-density tracers such as HCO+ show a redshifted absorption asymmetry reminiscent of inward motions. We construct a preliminary physical model of the circumstellar envelope (including radial density and temperature gradients, velocity field, and turbulence) that reproduces the observed line profiles and estimates the ionization fraction. The presence of both mechanical and (nonionizing) far-ultraviolet (FUV) radiative input makes the region an interesting case to study triggered star formation."

Star formation? Not surprising, deep inside the cave of a molecular cloud, but, if you'll pardon the pun, the plot thickens. The entire complex is about 1400 light years away from us at the perimeter of yet another massive molecular cloud, and at the same time it is situated on the frontier of a massive X-ray bubble located between the constellations of Cepheus and Cassiopeia. And that's not all. Thanks to hydrogen-alpha imaging, the whisper thin strands of an ancient supernova remnant near Cederblad 201 have also been detected.

Like a radioactive Roomba, the interstellar dust is being swept up as the expanding debris field moves toward where the Cepheus Flare lights the entrance to Wolf's Cave. These shocked molecular gas filaments were discovered in 2001 by John Bally and Bo Reipurth and belong to SNR 110.3+11.3; an unfathomably huge supernova remnant positioned only 1300 light years way, one of the closest known. Add to that the output of ancient planetary nebula Dengel-Hartl 5 and the celestial stew thickens even more. It is estimated all the elements will combine in about a thousand years and the product could very well ignite an incredible burst of star formation.

But, a thousand years is merely a blink of an eye in the grand scheme of things, isn't it? According to the 2007 studies done of the Wolf's Cave region by Edwin Bergin and Mario Tafalla; "Cold dark clouds are nearby members of the densest and coldest phase in the Galactic interstellar medium, and represent the most accessible sites where stars like our Sun are currently being born. Newly discovered IR dark clouds are likely precursors to stellar clusters. At large scales, dark clouds present filamentary mass distributions with motions dominated by supersonic turbulence. At small, subparsec scales, a population of subsonic starless cores provides a unique glimpse of the conditions prior to stellar birth. Recent studies of starless cores reveal a combination of simple physical properties together with a complex chemical structure dominated by the freeze-out of molecules onto cold dust grains. Elucidating this combined structure is both an observational and theoretical challenge whose solution will bring us closer to understanding how molecular gas condenses to form stars."

Carbonates from the planetary nebula, dust, exciting energy, photoelectric heating, polycyclic aromatic hydrocarbons, molecular gas... Where will it all end? What we do know is massive, bright star clusters are created from the giant molecular clouds. Will the Cepheus Torch one day ignite a brilliant stellar display from the mouth of Wolf's Cave? I wonder...

It wasn't until 1922 that NGC 2419 was finally determined beyond a doubt to be a globular cluster. For years the object baffled astronomers, who now also refer to it as the "Intergalactic Wanderer." The cluster's sky location is directly across from the Milky Way, which is unusual, but it's also extremely distant- some 300,000 light years from the Sun-and seems to be drifting through intergalactic space.

"Scanning the distances for globulars listed in Sky Catalogue 2000.0 reveals several other very distant objects, but none is even close to the brightness of NGC 2419," writes Walter Scott Houston in Deep-Sky Wonders. "Of the approximately 100 known globular clusters, almost all lie within a 65,000 light year radius of the galactic center."

The 'wanderer' is located about twice the distance from the Sun than the Large Magellanic Cloud, and magnitude estimates are between 9 and 10. Although it is one of the dimmest globular clusters, it is fascinating to peer at an object that is extragalactic.

Although this cluster can be picked up by smaller telescopes, it's quite a challenge, and we recommend using a 6-inch or larger telescope, especially if you're a beginner looking for it for the first time. NGC 2419 is located at RA 07hr 38.1m Dec. +38 53' 11.5M; at eastern end of 7-8 magnitude 2-star chain.

Below are two recent observations of NGC 2419 from seasoned observers. Take a stab at the March challenge object and share your own report in the review section of this article.

Roger Ivester, from his backyard in Boiling Springs, North Carolina:
When using my 10-inch at 191x, and averted vision, a very interesting feature was noted. The mostly round shape of the globular has a more concentrated area on the northern edge which creates a crescent shape. Can you see the brighter northern section? The following pencil sketch was made on a blank 5 x 8 note card with the colors being inverted using a scanner.

Kevin Ritschel of Orion, from Deep Sky Ranch, Paicines, CA:

Feb 22, 2014: SQM reading of 21.6

18" Custom Dob

6mm Eyepiece (305x)

NGC was immediately obvious in the eyepiece, easily recognizable as a round globular cluster. Myself and one other observer could easily see a "grainy" or sugar-bowl-like texture to the cluster. We both thought that the brighter members of the cluster would be intermittently observable, although the cluster was not "resolved" in the classical sense. While the cluster was "easy" in this size instrument, the member stars we were seeing was right on the limit.

Feb 23, 2014: SQM reading of 21.3

127mm f/7.5 triplet Refractor on Atlas Pro GoTo mount.

22mm ocular (43x)

5mm ocular (190x)

Using the GoTo, I slewed to NGC 2419, not necessarily expecting to see too much. But with 43x, the cluster was immediately obvious with direct vision! There are two fairly bright foreground stars, almost like a very wide double, that point directly at NGC 2419, the separations between the foreground stars and the distance to NGC 2419 are nearly identical making the entire asterism look like an exclamation point with a "fuzzy" period ( ..*). Since the globular was round and "fuzzy," it would have been easy to think this was a small galaxy; since there was no resolution of the cluster achieved, it would only have been the strong round symmetry that would cause someone to suspect it was not a galaxy.

At 43X, the cluster is visible with direct vision and quite noticeable. At 190x in this telescope, the cluster was so spread out that the cluster was far more difficult to see and the view was not satisfying (the power was too high for this small telescope and faint globular cluster).

Image of NGC 2419 by Jim Gianoulakis of Las Vegas:

Have you observed NGC 2419? Let us know what you see.

Often times you'll see these wide field photos of astrophotography images. One way to obtain a wide field photo of the night sky is to create a mosaic of smaller images. Adobe Photoshop has a tool called "Photomerge" and it's very easy to use to create wide field images of the night sky.

To get started, you first must take "overlapping" images so Photoshop will know how to stitch the mosaic together. Ideally, try to get approximately 20-25% overlap on each photo.

The example I have is NGC 2264. Here's the top image:

NGC 226 Image 1

And here's the bottom image:

NGC 226 Image 2

Before you merge your photos, crop any "stacking feathers" from your image. When you "stack" your image you typically see feathered edges and if you try to merge these feathered edges your merged photo will show a seam or line where the images overlap.

Remember, you shouldn't start processing your image before you merge the photo. After you've merged the photo then you can start processing your image. If you process each panel separately you will see differences and the mosaic will look like a bunch of stitched together patches.

In Photoshop simply select FILE'AUTOMATE'PHOTOMERGE, this will bring up a dialog box like this:

Click the BROWSE button and select your 16 bit TIFF files. I leave the layout to "Auto" and Check blend images together. Then press "OK" and let Photoshop do its magic! Now you may think it doesn't matter which order you select your files, but it does make a difference! In this example I selected the Bottom FIRST:

The results when selecting Bottom FIRST:

When I selected the "Bottom" first, it didn't give me the best crop results. I really would like to keep the bottom part of the image "square" because there are more important details on the bottom.

However, if I select TOP First:

The results when selecting TOP FIRST:

Now when I crop the image the bottom details will be square and I will have a nice mosaic.

Here are the results after I merged the photos and then processed the image:

Results - NGC226 Mosaic

If you would like to view this tutorial in a video, please visit Astrophotography Tutorials by Doug Hubbell on YouTube: http://youtu.be/NRkLtM-8h4M.

Astrophotography Tutorials by Doug Hubbell on YouTube: http://youtu.be/NRkLtM-8h4M

At Orion, we spend a lot of time under the stars. Sometimes we use a telescope, sometimes we use our plain old eyeballs, but much of the time, we keep both eyes open and use a pair of binoculars. Just about any type of binocular will show you something in the sky, but we generally use binoculars of 40mm diameter or larger; a lot of people prefer 50mm or larger. As with a telescope, the darker the sky, the more you will see, and you'll be amazed what you can see with binoculars under a dark sky!

Some have even said that two eyes are better than one. If you've ever used a pair of astronomy binoculars, you have every right to chime in with your opinion.

Orion 10x50 UltraView Wide-Angle Binoculars

Having a pair of binoculars on hand opens up an easy possibility: a quick, five minute view of the cosmos that doesn't require any sort of set up or telescope dragging. If skies are clear, you can fit this in before bed, or while walking your dog after dark. You'll be amazed at what you can see in just a few minutes under dark skies, and the expanded perception it will leave you with in the weeks to come.

Without further ado, here is Orion's Top 25 Showpiece Binocular Objects in the night sky. We know you have probably viewed the following objects in a telescope, but have you seen them in binoculars? Let us know in the "review" section of this article, or in a comment on this article on our Facebook Page.

Good luck!

Orion's Top 25 Binocular Targets:

Spring

1. M44, The Beehive
2. M81 & M82, a face-on and edge-on Galaxy Pair
3. M65 & M66, a Galaxy Pair
4. NGC 253 & NGC 288, a Galaxy and Globular Pair
5. M101, The Pinwheel Galaxy
6. M51
7. M108
8. Omega Centauri

Summer

9. M8/M20 Complex
10. M16
11. M17
12. M22
13. The North America Nebula
14. M27, The Dumbbell Nebula
15. M13, the Great Cluster in Hercules

Fall

16. M45, The Pleiades
17. NGC 869 and NGC 884, The Double Cluster in Perseus
18. M31, The Andromeada Galaxy
19. M33, The Triangulum Galaxy
20. The Helix Nebula

Winter

21. Orion Nebula, M42
22. Rosette Nebula
23. M36/M37/M38, a trio of Open Clusters in Auriga
24. M47/M46, a pair of Open Star Clusters
25. M78

Let us know if you were able to find any of these objects in binoculars, or have any favorites to add, by leaving a "review" of this article, or leaving a comment on this article on our Facebook Page.

You may have heard recently that the Sun's magnetic field has undergone a reversal. It's true. While this though may sound a little terrifying, the fact is that our Sun does this about every eleven years or so. It's part of what is known as the solar cycle. During the flip, there is often solar activity like flares, which can affect space electronics, but we have safeguards in place for most flares. And while weather can be affected, the effects are usually subtle.

The first evidence of this solar cycle was seen in the early 1600s, when observations of sunspots showed there were periods of more and less sunspots. By the mid 1800s it became clear that sunspot frequency generally oscillated over a period of about 11 years.

Map of magnetic field lines on the Sun. Credit: NASA

We now know that sunspot activity is driven by the Sun's magnetic field. The sunspot cycle is just one consequence of the variations in the Sun's magnetic activity. When the Sun's magnetic field is quiet, there tend to be few sunspots. When the Sun's magnetic field is particularly active, there tend to be lots of sunspots, as well as other things like prominences and solar flares. It is during this active period that the Sun's magnetic field will undergo a reversal.

We're not entirely sure what causes this reversal. But we do know the Sun's magnetic field is due to a magnetic dynamo in its interior. The flow of charged plasma induces the magnetic field, similar to the way a flow of current in a wire produces a magnetic field. Changes in the behavior of that dynamo is what leads to the solar cycle. But the mechanism behind those changes is unclear.

Part of the difficulty in understanding these reversals is that while they usually occur roughly every 11 years, they do not occur like clockwork. There are cycles that are a bit shorter and a bit longer. Also, the Sun can enter extended periods of lesser activity. For example, from about 1790 to 1830 there was a period when the oscillations were smaller, and the periods of maximum sunspot activity were less intense, known as the Dalton minimum. We're not entirely sure why such minimums occur either.

Magnetic Loops on the Sun. Credit: NASA

Interestingly, our current solar cycle (known as cycle 24) has been noted to have some similarity to the early stages of Dalton minimum. Before the Dalton minimum, cycles got successively smaller, with the same drop to about half the activity that had been typical. If we follow a similar pattern, then cycle 25 will be about the same as cycle 24, and we will have several decades period of a relatively quiet Sun. What does this mean for humans and the Earth? Low solar activity correlates with slightly cooler temperatures, but that's about all people might notice. Our atmosphere is a pretty good barrier to anything dangerous.

But now that the Sun's magnetic reversal has occurred for this cycle, we know we're about halfway through the solar maximum. You can expect word of the next magnetic reversal to hit the news in about 11 years.

Did you know that the magnetic poles of the Earth also flip? The last time it flipped was 700,000 years ago, according to evidence found in geological strata. What will happen when it flips again? That is not entirely clear, but scientists have many speculations. Stay tuned for my next article on geomagnetic reversal.

Read more articles by Brian Koberlein here.

CAUTION: Never look at the Sun, either directly or through a telescope or binocular, without a professionally made protective solar filter installed that completely covers the front of the instrument, or permanent eye damage could result. When using a truss tube telescope to view the Sun, both a properly fitting solar filter and light shroud are required.

Planetary photography can be very interesting and rewarding. We are lucky to have several planets in our solar system that are bright enough at various times of the year to see and photograph. Our solar systems most massive planet, Jupiter, is one of those, providing some breathtaking views and images. The planet features colorful bands, a Giant Red Spot, and four bright moons that are easy to see and capture in images.

The first thing you will need to photograph Jupiter effectively is a telescope with a relatively long focal length. I have an Orion APO refractor with 480mm of focal length, but that simply isn't enough to capture any noticeable detail on Jupiter's surface. That is more of a wide-field scope for things like galaxies, star clusters, and nebulae. My other telescope is an Orion Maksutov-Cassegrain model with 2700mm of focal length. Now we're talking! I would say that a focal length of around 1500mm would be the minimum that I would recommend for planetary work.

Credit: Stephen Rahn

Now what kind of camera should you use? Some prefer to connect a DSLR or Micro Four Thirds camera to the telescope and shoot in what we call prime focus. I have done that a few times myself, but the general consensus is that a CCD camera is a better option. I use an Orion Planetary Imaging Camera and I have had excellent results with it. A CCD camera is rather small and you will need to connect it to a laptop during your imaging session. The camera displays your target on the laptop, and you will use special image-acquisition software on the laptop to shoot videos of your target. Why shoot video? The idea is that you want to capture a lot of detail, and video offers hundreds (or thousands) of frames. You then use a stacking program such as AutoStakkert, AviStack, or RegiStax to align and stack your video frames. This will (hopefully) produce a nicely detailed composite of your video frames. You can then take that composite image and edit it in Photoshop, Lightroom, or any other image-editing program you prefer.

Another consideration for shooting a planet is how high it is above the horizon. When an object has just come up over the horizon, you will be observing it through a lot more of Earth's atmosphere than if it were up higher in the sky. So don't try to image Jupiter just after it has cleared the trees. Wait until it's at least about 45 degrees or higher if possible so you will be dealing with less atmospheric interference. Here is an example of a shot of Jupiter when it was just coming up.

Credit: Stephen Rahn

You can make out the bands, but they are pretty blurry.

Now here is a better shot that was taken when Jupiter was much higher in the sky.

Credit: Stephen Rahn

Here you can see much better detail and you can even see three of the Galilean Moons. Two are on the left and one is on the right.

Once you've set up your scope, connected the camera, and pointed at Jupiter you will now want to make sure that your focus is as accurate as possible. Poor focus will mean you get a blurry image and that is incredibly frustrating. You might want to consider a dual-speed focuser if you don't have one. I have a dual-speed Crayford focuser and it lets me do very fine adjustments to the focus and that has really helped with the quality of my images.

After you've gotten focused, it's now time to start shooting some video. Check to see how many frames per second your camera can shoot, and start with a video that will capture 500 frames. If your camera shoots at 15 frames per seconds, that's about 33 seconds of video. You might be surprised at how good of an image you can get from a video of that length.

Now that you've got a video file, you will have one of those stacking programs align the video frames and then stack them into one composite image for you. Consult the documentation for the program that you are using. I have found that I get the best results from AutoStakkert, but others prefer RegiStax or AviStacker. It couldn't hurt to process the same video file with multiple programs and see which one comes out best. I often do that myself.

When you finally get a composite image, feel free to use Photoshop, Lightroom, or whatever your favorite image-editing program is to do some processing. I often use the sharpen and levels adjustments to refine the image and try to bring out as much detail as possible. If your image isn't that great, try shooting 1,000 frames next time. If your focus is good and Jupiter is high enough in the sky you should be able to get some pretty good images.

After you've gotten some practice with Jupiter, try your hand at the other bright planets. Saturn and Mars will being coming into the night sky this spring, and they make excellent targets as well.

Happy shooting and clear skies!

Do you have any questions or experiences to share about imaging Jupiter? Share them in the 'review' section of this article.

A bright supernova has appeared this week in the galaxy known as M82, or the "cigar galaxy." M82 is a starburst galaxy about 12 million light years away. On a cosmic scale, this is right in our backyard. In fact it is the closest supernova we've had since 1993.

If you've ever wanted to view a supernova (and you live in the Northern hemisphere) then now is your chance. M82 is in the constellation Ursa Major. If you find the big dipper, then it is diagonally up and away from the handle about the distance of the pan. Click here to consult star chart. It is a bright galaxy, so it is pretty easy to find with a pair of binoculars or a small telescope. This new supernova about magnitude 11, so is bright enough to view with a small telescope. See observing sketch of M82 SN by Roger Ivester, 1/22/2014.

The new supernova: E. Guido, N. Howes, M. Nicolini.

Although news of the supernova has just hit the media, we already know a few things about it. From its spectra we know it is a Type Ia supernova. The traditional view for Type Ia Supernovae is that they are the result of an interaction between a red giant and white dwarf in a binary system. A white dwarf is a star so dense that only pressure of electrons keeps it from collapsing under its own weight. But electron pressure can only hold up against the weight of gravity to a point: known as the Chandrasekhar limit, this is about 1.4 solar masses. If a white dwarf is in a close orbit with a red giant, some of the outer layer of the red giant can be captured by the white dwarf. The white dwarf then gains mass until it is pushed past the Chandrasekhar limit, resulting in runaway fusion that causes the white dwarf to explode.

But new evidence indicates that Type Ia supernovae are due not to a white dwarf being pushed past its limit, but rather due to a collision of two white dwarfs. Often, two white dwarfs in a close binary have a third star orbiting the pair. As this third star gravitationally interacts with the binary dwarfs, it can cause their orbits to degrade to the point where they collide with each other. The resulting explosion produces the supernova.

Type Ia supernovae are particularly useful to astronomers because they always explode with a similar luminosity. This means we can observe how bright the supernova appears and compare it with the actual brightness to determine its distance. Supernovae such as this one help astronomers determine the distance to M82 and other galaxies as distant as billions of light years.

Illustration of our understanding of a white dwarf binary leading to supernova. Credit: NASA.

Whenever a "close" supernova occurs, there's often speculation about when one will be visible in our galaxy. It turns out we're long overdue for one. In November of 1572 Wolfgang Schuler observed a supernova in the constellation of Cassiopeia. A few days later it was observed by Tycho Brahe, who began taking careful observations of this visiting star, which came to be known as Tycho's supernova. About 30 years later, in 1604, Kepler observed a supernova in the constellation of Ophiuchus. Since then, there hasn't been an observed supernova in our galaxy, which is unfortunate and a little perplexing.

Studies indicate that a galaxy of our size and type should have a supernova about once every 50 years. That we haven't seen another in 400 years seems to indicate that there's a crucial aspect of supernova physics we don't understand. Either that, or astronomers are having a 400 year long streak of bad luck.

Another topic that often gets raised is whether a supernova could occur close enough to threaten life on Earth. It turns out there is no need to worry. Although supernovae can outshine an entire galaxy at maximum brightness, one would probably need to be closer than 100 light years or so to pose any threat. Of the stars we know that could become a supernova, the red giant star Betelgeuse is perhaps the closest, at a distance of 650 light years. At some point in the next several millennia Betelgeuse will go supernova, and when it does it would have an apparent magnitude of about -11. That is brighter than any star or planet in our sky, but it isn't quite as bright as a full moon.

So even if Betelgeuse does explode in the near future, it won't be the end of the world. It will just be a short lived beacon in our night sky, casting shadows on moonless nights.

Have you observed the supernova in M82? Let us know if you see it, and what you used to find it.

Read more articles by Brian Koberlein here.

By David Jay Brown

For fans of the science fiction film Contact--where a scientist played by Jodie Foster establishes communication with an advanced extraterrestrial species, the SETI Institute has almost mythic status.

However, SETI, which means "Search for Extraterrestrial Intelligence"--is the acronym for a very real organization which scans the skies every night in search of some type of evidence for the existence of intelligent extraterrestrials-in hopes of establishing contact.

Becoming an official nonprofit corporation in 1984, SETI's mission is to "explore, understand and explain the origin, nature and prevalence of life in the universe." Using optical and radio telescopes, SETI's team of determined astronomers and communicational specialists seek the answer to one of mankind's most gnawing question: are we alone in the universe?

Allen Telescope Array (ATA) at the Hat Creek Observatory in Northern California scans known planetary systems for signals. Credit: Seti.org

Seth Shostak, Ph.D., is the senior astronomer for the SETI Institute, based in Mountain View, California. He hosts the popular weekly radio show "Big Picture Science," and is also widely recognized as a science educator. In 2004, Shostak won the prestigious Klumpke-Roberts Award by the Astronomical Society of the Pacific in recognition of his "outstanding contributions to the public understanding and appreciation of astronomy."

I spoke with Shostak on January 16, 2014. In conversation, Shostak combines open-mindedness and skepticism with a vast array of knowledge, and he is especially talented at seeing the "big picture." In the following interview of Shostak, he talks about SETI's current search for life in our galaxy, whether or not he thinks alien civilizations are benevolent, SETI's plans for the future, and what amateur astronomers can do to help in the search for extraterrestrial intelligence.

David Jay Brown: How did you first become interested in astronomy and the search for extraterrestrial intelligence?

Shostak: That all began as a kid, of course. I was interested in astronomy from the age of 8, since I was looking at a book that my parents had. It was an atlas, but in the back of the atlas there was a funny-looking diagram, which I didn't understand.

So I asked my mom about it, and she said, "Oh, that's a diagram of planets."

I had never heard the word "planets" before, but once I heard it, I got interested in that--and by the age of 11, I had built my own telescope.

As far as aliens go, well, that was also, I'm sure, from about the age of 8--because there were a lot of science fiction films in the movies those days featuring aliens. Aliens were always doing something terrible to humanity in these films--and I went to them all!

Brown: Can you tell us about some of the latest projects that SETI is working on?

Shostak: Our SETI projects are multiple. We use the Allen Telescope Array--with a large number of small dish antennas--so we're doing what's called "radio SETI." That's looking for the kinds of signals that transmitters would make.

We have another project where we're looking at the galactic center. That's something that I think is a good idea, because that's a special place in the Milky Way. Incidentally, my first published SETI experiment--in 1981--was to look at the galactic center, the center of our galaxy.

A really advanced society would know that everybody is going to be looking at the galactic center sooner or later--so they might put a big transmitter there to act as some sort of beacon. So we're doing looking there.

We're also looking at star systems that are known to have planets. Of course we do that. I wrote an article about this that's in the January issue of Astronomy magazine actually, about looking for signals from the neighborhoods of red dwarf stars.

I honestly think that that's a very good SETI strategy, because probably 1 in 5--certainly 1 in 6, at least--of red dwarf stars, will have a habitable planet orbiting around them, it seems. Red dwarf stars are also so numerous, and so old, that they're just perfect for a SETI search.

Brown: What research techniques do you think hold the most promise for establishing contact with a race of intelligent extraterrestrials?

Shostak: Of course nobody knows that. If we knew that, then we would put all our resources into the most promising techniques.

We're great fans of radio SETI, and that's the traditional form of SETI. That was used in the first SETI experiment, at least the first modern SETI experiment. It was a radio search in 1960 by Frank Drake.

Then we continued to do that, because--in terms of the energy required--it turns out, it's very easy and inexpensive to send bits of information from one star system to another using radio. So I do like that.

But it's also the case that optical SETI appeals to me, and I think that it will appeal to me more in another couple of years, when we have new detector technology that would allow us to survey the sky much more quickly, in the optical.

But there are also other things that are coming down the pike, if you will. These are the kinds of SETI experiments where you don't actually deliberately look for ET, as it were, but you mine data collected by other sorts of instruments. For example, large telescopes that are intended for other purposes, but might in fact reveal the activities of very advanced societies.

There could be engineering projects that are big enough for you to see. So those are, all to me, very interesting techniques.

Brown: Taking the recent discoveries of so many exoplanets into account, how common do you think intelligent life is in the universe?

Shostak: Well, that's a complete guess, but it's now looking like there are roughly a trillion planets in the galaxy. The current estimate is that 1 in every 5 stars has an earth-like world. If that's true, then there are on the order of 50 billion "Earths" in the Milky Way galaxy.

Now, what fraction of them have life? I bet most of them have life, actually. But what fraction have intelligent life? That is a different question. But even if it's one in a thousand, then that's still 50 million societies that have sprung up in the galaxy--a galaxy that we know for sure has supported intelligent life at least once.

So if intelligent life has any durability at all, if it can last for a million years, or something like that, then that means there are tens of thousands of worlds that are extant today, that are out there now with cosmic confreres, with intelligent beings.

That's a big number.

Brown: What type of patterns are you (or your computers) listening for when you search through the radio signals in the sky?

Shostak: It's actually very simple, because the searching is done by the computers. Of course there's a tremendous amount of data coming in. There's really a fire hose of data coming in, so you can't look for the Fibonacci series, or anything like that.

In fact, you wouldn't get it anyhow. Because you're adding up the signals coming in over a period of minutes, any sort of fast modulation or any sort of message would get smeared out anyhow.

But we're just looking for the kind of signal that a transmitter would make. A transmitter would make a signal that would have some narrow band component. It would have peaks of energy over a very narrow range of frequencies.

That's exactly what television, radar, and radio do as well. The energy is put into a narrow range of frequencies, although it is more narrow for AM than for FM. But it's still pretty narrow. So that's the kind of signal that we look for--narrow-band signals--and if we find one, and if the source is moving across the sky at the same pace as the stars, then you say, "That's not a bit of nature. That's not a pulsar, a quasar, or anything like that--it's too narrowband. That's some sort of artificial source."

Brown: Physicist Stephen Hawking has warned us not to attempt extraterrestrial communication, because he thinks that it makes us too vulnerable to the will of an advanced species, and in his new book, The Future of Mind, Michio Kaku says that you once told him that any battle between ourselves and an advanced civilization would be like a battle between Bambi and Godzilla.

How do you envision the friendliness of other intelligent species in our cosmos? Do you think that our science fiction films are paranoid, and that the universe is basically a friendly place, or do you think that we need to proceed more cautiously, and be concerned about the dangers of an intelligent extraterrestrial species, many years more advanced than ourselves, that may be seeking to exploit us or use our resources?

Shostak: To begin with, I don't think they would be interested in our resources. What do we have that they don't have much nearer by? But, aside from that, the facts are that we can't guess the sociology of the aliens.

A lot of people like that the idea of malevolent aliens, and in particular Hollywood likes it, as, of course, friendly aliens are a lot less interesting than hostile ones from a movie's point of view, so they have a vested interest in hostile aliens. As far as Stephan Hawking's point goes, I've written three articles on that. You can actually find one if you go to The Edge, for example. I wrote an essay last year about what I'm not afraid of, and I'm not afraid of that, largely because of the following:

You can't say whether the aliens would be friendly or hostile. I suspect most of them would be friendly, because, after all, I think advanced societies probably tend to be peaceful, otherwise they don't last very long.

But hey, I could be wrong. And in fact, if only 1 percent of them are not friendly, well that might still be dangerous. But my point is somewhat different. It's very easy to show that any society that has the ability to come here, and do some damage...(laughter) If they can do that, if they've got the technology to do that, they also have the technology to pick up all the signals we've been broadcasting into space since the Second World War.

So there's actually no point in being careful about this. There's no point in turning off the radar systems at the local airport. All that would do is kill people, and it's not going to make us any safer--because those signals are already on their way. And any advanced society, anyone that could ever pose a threat to us, could pick those up anyhow.

Brown: What does SETI plan to say to the first intelligent extraterrestrials that it makes contact with?

Shostak: I suppose we would just send a whole bunch of information, if we were to be responding to a received signal. Mind you, there's a protocol that says you wouldn't respond to a received signal without international consultation, and probably that means something like the United Nations... To be honest, I don't think that it matters. I honestly don't think it matters, because you could have said that maybe the natives of the Caribbean should have prepared what they were going to say to Spaniards in 1492, should their ships ever show up on the beach. It really didn't matter what they said actually.

Brown: Please tell us about the SETI Institute's radio program "Big Picture Science" that you host.

Shostak: Yes, it's a weekly show about science. We always try and put the show in the context of the overall picture of science, the overall picture of humanity, and what it means. We explore the scientific developments, and also ask how does that affect us in any way? So that's the kind of thing we do, and we try and make it fun. We have lots of very good scientists, lots of Nobel Prize winners, and so forth. We interview about 4 or 5 people every week. You can find us on the web at: www.bigpicturescience.org

Brown: What are some of the future research projects that SETI has in mind?

Shostak: Unfortunately, the future depends a lot on funding, but we would like to continue to increase the capabilities of the Allen Telescope Array, which is the instrument that we use.

This is because that would speed up the search, and speeding up the search means that, if there's going to be success, it's going to come sooner rather than later.

And as I say, there are these new approaches. I like the idea of optical SETI using two dimensional detectors.

I see that coming in, as something that right now is mostly waiting on technical developments that we won't make, but industry will.

Also, I have to say, I think that data mining would be a very interesting thing to do. There are some very big optical telescopes being built around the world, and they will provide enormous data sets that can be combed by anybody with a laptop and a little bit of time to look for anomalous features, things that aren't natural.

Brown: How can people at home get involved with SETI, using their personal computers?

Shostak: On our website we have something called SETI Live, where people can look at some of the actual data. People who are interested in participating should just look for interactive SETI programs with their internet browsers and check them out. It may be something that they want to do.

Brown: What excites you most about the search for extraterrestrial intelligence?

Shostak: That's a big picture question. I think that's the most exciting thing. This is something that everybody has some interest in. I mean, are we the only game in town? Are we the only kids on the block? Are there other kids? And if so, what are they like? I think everybody's interested in that. And of course no previous generation could answer this question, but we can--so, hey, that's exciting!

Read more Orion articles by David Jay Brown here.

If you're interested in investing in a pair of binoculars for observing both starry vistas and terrestrial subjects, then you might want to take a look at the Orion Giant View 15x70 Astronomy Binoculars. These porro-prism beauties are well designed, rugged and very versatile. What's more, they've been engineered to give lasting performance.

Weighing in at a hefty four pounds, the Orion Giant View 15x70's have been reinforced with an aluminum rod and the objective cell frame has also been beefed up for maximum structural rigidity. While this adds weight, it also ensures that no matter how many times these binoculars are flexed open to accommodate being stored, or adjusting to individual eye separation distances, they are going to remain in alignment. No one wants to pay good money for a pair of binoculars that feel like they are going to come apart where the barrels are hinged together! There is also a captive sliding 1/4"-20 mounting post located on the rod - a big bonus when considering mounting the binos to a tripod.

The next thing you'll notice about the Orion Giant View 15x70 Astronomy Binoculars is that each eyepiece is individual focus - a change over the traditional right eye diopter. This facet of the Giant View 15X70's construction means you get a more improved focusing precision over center-focus mechanisms, however you may wish to secure the binoculars to a mount and tripod arrangement to take advantage of this unique feature.

Another high quality addition is the BAK 4 prisms and internal baffling. This provides for excellent image contrast and sharpness. You'll also find the full multi-coatings to be exceptional - reducing glare and offering excellent color correction. The 4.6mm exit pupil is right on par with the average adult maximum exit pupil, and 18mm of eye relief means you're not dangling the binoculars out in space to see through them, nor do you have them crammed against your eyes.

The Orion Giant View Astronomy Binoculars come with a heavy duty aluminum case.

As for the view? At 15X and 70mm of aperture, you're enjoying a vision comparable to a small refractor telescope. However, instead of a constricted field of view, you're checking out a full sixty degree apparent field of view and a very nice four degree angular field. For astronomical purposes, that means being able to follow an extensive comet tail, or being able to take in expansive nebulae regions and admire large star clusters. The Orion Giant View Astronomy binoculars are quite capable of picking up brighter galaxies, too! Put these binoculars on a tripod and you'll be able to resolve out wider double stars and take on some serious crater action when it comes to the Moon. Don't forget the planets! Not only are they are capable of revealing the four Galiean moons of Jupiter, but you'll also be able to spot the shape of Saturn's ring system, reveal the orb of Mars, catch the bright form of Venus, pick Mercury out of the dawn or dusk and capture the distant twinkle of Uranus.

Hang on, because the Orion Giant View 15X70 binoculars are good for more. Pass them on to a hunter and they'll be delighted with the close-up view of distant game. You'll be able to see the foraging deer and spot antlers. With the 70mm aperture, you'll enjoy exceptional low light resolution. This is especially helpful at dawn and dusk when they are on the move. Maybe birds are more your thing. If so, set a pair of these big binos on a tripod and train them on a feeder. You'll feel like you're feeding with the flock! There's more. The Orion 15X70 Giant View binoculars also come with a deluxe hard case. You'll appreciate its added security. Now you can safely keep your binoculars with you in your car's trunk, take them along as carry-on luggage on an astronomy expedition, or add them right to your gear for hunting, hiking and camping trips.

Have you used Orion's 15x70 Giant View Astronomy Binoculars? Let us know how you liked them in the review section of this article.